Jeff's DIY

Advice on doing your own diagnosis and repair

Advice from the book Can I Do It Myself?

Engine Operation Issues


How to Fix Poor Idle, High Idle, Stalling On Fuel Injected Gas Engines

This tip provides some generic troubleshooting and repair tips for a fuel injected gas engine that stalls or hunts at idle.

Often this condition does not result in the computer's detection of a malfunction. However, if your engine light is on, I always recommend getting a free scan at your local parts chain to help diagnose the problem.

A low idle or stalling engine can be caused by a number of things. First of all, make sure your vehicle has good spark plugs, ignition wires, and distributor/rotor (if equipped). Other possible causes include the following:
1. Vacuum leaks either in vacuum hoses or intake manifold gaskets.
2. Rich mixture caused by torn fuel pressure regulator diaphragm or failing MAP sensor (skip the check if your mixture is not rich)
3. Insufficient idle air flow due to clogged passages or failing idle air control valve/motor
4. Excess EGR flow, caused by a stuck open EGR valve
5. Excess EVAP system flow due to a stuck purge valve

A hunting idle is usually caused by a blocked PCV valve.
A high idle is generally due to a failed idle air control valve. If this is your symptom, first check to make sure the throttle cable has a little slack, is correctly attached to the throttle, and the throttle is able to close fully. See pictures below:

typical throttle cable


throttle body assembly


If the throttle is closing well but the idle is high, skip ahead to the section on IAC.

For a low idle, the above list of 5 checks are in order of difficulty and likelihood to be the cause, so this is a good order in which to perform checks, unless you have additional knowledge that makes something lower on the list more likely to be the cause. I will go thru each item for a generic engine in the order 1-5.

1. Vacuum leaks cause the engine to run lean and draw too much air for an idle setting of the throttle. Vacuum leaks can also cause an automatic transmission to shift late and can sometimes cause a vacuum powered heater mode control switch to fail, leaving your ducts in a default flow mode. An engine that will not idle due to a vacuum leak generally has a pretty good leak that you can often hear by walking around the engine. Check the big hoses first, like the one to the brake booster. Then check every other hose connected to the engine intake manifold. Check both ends of every hose for a poor connection and repair or replace any leaking hoses. Although rare, a leaky intake manifold gasket can also cause an engine to stall, but usually a leaky gasket will set a trouble code P0171 and/or P0174. To check for leaky gaskets, start the car and spray carb cleaner at the intake manifold gaskets. If the engine revs, you have a leak. If you have an upper as well as a lower intake manifold, check both sets of gaskets.

2. Torn fuel pressure regulator diaphragm: If you know your car is not running rich or you do not have a vacuum powered regulator, you can skip this step.

Many fuel injected engines use a vacuum actuated fuel pressure regulator on or near the injection rail or inside the throttle body (in the case of throttle body injected engines). The vacuum reduces fuel pressure when the engine is not in high fuel demand. However, since the intake manifold is the source of vacuum for these type regulators, when the diaphragm tears, it allows fuel to be sucked through the regulator directly into the intake manifold, thus causing a rich fuel/air ratio. The picture below shows a regulator spitting gas from the vacuum port due to a torn diaphragm.

Faulty fuel pressure regulator


To check a regulator on the rail, pull the vacuum hose off the regulator and plug the hose with a golf tee. Start the engine and watch for fuel to come out of the regulator vacuum port. If fuel comes out, replace the regulator.

For throttle body injected (TBI) engines, the regulator is usually integrated into the throttle body. The regulator may be on the side or actually under the flat filter interface, and the cover may be domed or flat and may or may not have an external vacuum port. Typical TBI fuel pressure regulators are shown below along with a diaphragm:

TBI pressure regulator

TBI pressure regulator



Regulator diaphragm


Remove the 4 screws and the diaphragm will be exposed. Note the orientation/appearance of the diaphragm so that you get it back in right after inspecting or replacing it. Inspect for tears and replace any suspect diaphragm.

3. Idle Air Control (IAC) Valve: Just as controlling idle speed is difficult with carbureted engines, it is also difficult with fuel injected engines. Because the engine is rotating slowly, the fuel/air ratio and flow must be carefully controlled to keep the engine running even as there are changes in temperature and load (such as the air conditioning compressor turning on and off). Fuel injected engines use a number of sensors as input and the engine computer adjusts both injector pulse and idle air flow. The flow at idle is usually controlled by the idle air control valve, which is a cone-shaped end on a stepper motor-driven screw. Much like a common garden spigot, the cone blocks or allows flow according to the automated screw adjustment. The flow paths and valve tip can become dirty over time and limit the system's ability to control the airflow as precisely as necessary. The motor can also blow a winding or wear out such that it does not step as commanded by the computer. A quick test to verify the operation of the valve is to start the engine, observe the idle speed, and pull off a vacuum hose (like the one leading to the brake booster). The idle speed should rise, and then fall as the IAC motor tries to compensate for the vacuum leak. Next, reattach the vacuum hose. The idle should drop, and then stabilize. If the engine reacted as indicated, the circuit is probably OK.

Remove the valve and clean the passages and valve with carb cleaner or a similar solvent. Do not submerge the motor in solvent. The valve may be sealed by a gasket or o-ring or both. Be sure it seals properly when reinstalled. If your valve did not react properly during the crude test, check the continuity across the stator and armature windings of the motor. If either winding shows an open or high resistance, replace the valve. Also, if the valve is loose in the motor, the bearings are probably worn out. Remember, this is a precise valve and must hold close tolerances. Some typical installations are shown below along with an IAC valve.

Idle air control valve


EGR valve

New idle air control valve


4. EGR Valve: The exhaust gas recirculation system is required by many engines to meet national or California emission standards. When the computer deems the conditions appropriate, it opens the EGR valve and controls the flow of exhaust gas back into the intake manifold to provide inert mass that absorbs the heat of combustion, thereby reducing NOx products. There are many variations of EGR systems, and the valves may be controlled by vacuum, electric motor, or electric solenoid. Many systems include a sensor to feedback either flow or valve position to the computer. Most computers do not open or extremely limit the EGR valve opening during idle because of the difficulty in controlling idle mixture. The default position of the valve is closed. However, if the valve has not closed properly from off-idle operation, the EGR flow can cause a rough or poor idle. If necessary, use a manual for your vehicle to obtain a procedure for removing, cleaning and testing your EGR valve. At a minimum, make sure the valve is able to close with no control forces applied. Some typical EGR valves are shown below. The valve is usually mounted in the intake manifold and exhaust gasses are either routed through the heads to the intake manifold exhaust passage or they are piped to the valve from the exhaust manifold.


EGR valve attachment


EGR valve attachment


5. EVAP Purge Valve: The evaporative emission system is designed to limit the release of fuel vapors from the fuel tank. Up to a certain design pressure, vapors are stored in a charcoal canister and are later drawn into the engine to be burned. The computer determines when conditions are appropriate for vapors to be allowed into the engine and opens the purge valve with precise solenoid pulses. As with the EGR valve, the computer stops or severely limits the flow during idle. However, the valve may become stuck, inoperative, or clogged with charcoal bits (if the canister is leaking its charcoal). This valve may be difficult to find, though it is usually mounted on the intake manifold, throttle body, along the air inlet hose or on the charcoal canister itself. If you aren't sure you have found it, trace the hose back to find the canister. Remove the valve, clean it with carb cleaner, and check that it closes on its own. If you have a manual that provides tests for the valve, run the tests to verify proper operation. Some typical installations are shown below.

Typical evap purge valve

evap purge valve mounted to canister


If you have performed all of these checks and steps and your car still idles poorly, consider reviewing my tips on misfires.


Causes of Gasoline Engine Misfires

Misfire issues can generally be categorized as localized or random. A localized misfire in my definition would occur on at most two specific cylinders. In OBD II diagnostic code terms, that would be 2 trouble codes of the form P030x and P030y; whereas a code P0300 or several different codes P030a, b, c, etc. would indicate a random misfire issue. These two different categories of misfire call for different troubleshooting procedures. In each case, however, the cause of the misfire can be electrical or air/fuel related and can also be continuous or intermittent. I will start with the localized case, so if you have a random misfire, please skip ahead to that section of the post.

Single-cylinder or localized misfire troubleshooting:
The easiest thing to check is always the secondary electrical circuit.
Caution, high voltage ignition sparks can hurt you, but the most serious injuries happen when pulling back when shocked and striking something else with your elbow, like the hood of the car. A single spark is not dangerous to a healthy person, but I always prefer to avoid getting shocked. When testing the ignition wires, coil, or plugs, use an insulating mitt or tool or at least make sure a better ground than your body is available for the spark to jump to.

Electrical checks:

If you don't have the diagnostic codes for the misfire or just don't know which cylinder is misfiring, methodically pulling the wires from the plugs on each cylinder in turn is a good way to find the bad actor. When doing this, pull the wire off and away from the plug and let it jump to engine ground. If sparks are jumping, move the wire back and forth from the plug to engine ground and listen for changes in the engine rpm. If there is no change in engine rpm with the wire on versus off the spark plug, that cylinder is misfiring.

Once the particular cylinder(s) misfiring have been identified, you can test both the coil and wire by pulling the wire boot slightly off the plug in question--you can hear the spark jumping to the plug. If your misfire is continuous on this cylinder, you would hear no sparks at all. If the problem is intermittent, listen for missed sparks. If you identify a cylinder with a spark misfire, try swapping wires and coils to determine if the problem is in the wire or the coil. If the problem is not in the wire or the coil, check the distributor (if you have one) for a bad inside terminal and also pull and test the spark plug by putting it back in the wire, grounding the threads, and cranking the engine to check for a good spark at the gap (you might want to pull a few wires off the other plugs to avoid having the engine start with the plug out, as this can be very noisy). If all of the electric components seem good, move on to check the cylinder internals.

Fuel injector:

Put a long screwdriver on the injector and put the other end against your ear while someone cranks the engine. If the solenoid is not clicking regularly, suspect a bad injector. It is also possible the injector is plugged or dirty. This condition is difficult to diagnose, but if you suspect this you can remove the fuel rail and clean the injectors per the manufacturer's procedure.

Compression test:

Buy or borrow a compression tester. Remove several spark plugs, including the one(s) that are misfiring. Screw the compression tester into the plug socket hand light (or hold the tester in the hole if it has a rubber taper end), and have someone crank the engine through several revolutions. Read and record the pressure on the gage, release the pressure in the gage and go on to the next cylinder. A reading of less than 50 or so psi can cause a misfire. A low reading can be caused by a burned valve, a blown head gasket, or possibly an over-tightened rocker arm/inadequate valve lash, among other more remote possibilities. The latter case (rocker arm) usually only occurs after head or valve work was recently done on the engine and was followed by improper valve lash adjustment. Except in this case, the cylinder head must be removed for repair. A low pressure reading on adjacent cylinders is a clue that the head gasket is blown between the two cylinders. Additional clues as to the type of failure may be gleaned from careful inspection of the spark plug.

Random misfire troubleshooting:
The engine computer sets diagnostic trouble code P0300 when the crankshaft position sensor indicates rpm hunting under constant external conditions. Therefore, it is very difficult to distinguish genuine misfiring cylinders from generalized rough running.

Random electrical misfire:
If the cause is electrical, it is in the ignition system that produces the signal to the coil(s). In older engines, this might be due to a failing ignition modulator or pickup coil in the distributor. In modern engines, it might be a loose, failing, or poorly connected crankshaft position sensor (or camshaft position sensor in engines that use this sensor for spark timing). This condition may or may not set an OBD II trouble code. Because of the large variation in ignition systems, I recommend you get the wiring diagram for your ignition system to see what components may be the cause of an inconsistent ignition signal to the coil(s). In rare cases, the problem may be with the modern ignition control, engine control, or powertrain control module. The problem may also be with general deterioration of the ignition wires. This condition can be verified by running the engine in a dark environment and watching for sparks jumping off the coil or wires.

Air/Fuel causes of a random misfire:
For the issue to be identified as a misfire, the changes in conditions in the cylinders must be rapid rather than gradual (such as in the case of a hunting rpm). These kinds of changes may be caused by unsteady airflow in the intake or inconsistent injector operation. Always check for a clean throttle body and idle air passage as well as idle air control motor operation. Also check the EGR valve operation and flow path. There may be specific tests you can run on these valves for your car. Consult a manual if you want to check these out carefully. Most of these components can be cleaned with good old-fashioned carb cleaner. It's also a good idea to make sure your vacuum operated fuel pressure regulator (if you have one) isn't drawing fuel into the intake manifold through a torn diaphragm.

Random injector issues are rare but may be caused by dirty fuel or worn out injectors. Another possibility here is a camshaft position sensor malfunction, but this will usually set a trouble code. In rare cases, injector timing and pulse width irregularity can be caused by the computer itself.


My Ignition Coil Doesn't Spark

An easy way to check for spark is to pull an ignition wire from the coil or distributor and hold it with an insulator (oven mitt or pliers with plastic grips?) close to the terminal you removed it from while someone cranks the engine. You may have to push the wire into the boot to expose the terminal or use a Phillips screwdriver to reach into the terminal to get the spark out of the boot. Here is what that might look like:

Spark from plug wire


If sparks jump across when cranking the engine, you have fire. If you have fire at the coil/distributor, you must still verify that the ignition wires are properly connected to the spark plugs. This is especially important in cases where the plugs or wires were replaced just prior to the "no start" condition. Look up the firing order specifications for your engine and verify that the wires are connected in order. See my tips on firing order at. If all of this is good and your engine still won't start, refer back to my tips on "no start."

If you do not have fire, use a (12 volt) tester to check the coil terminal for ignition power. The coil voltage varies from car to car, but should be between 9-15 volts. If there is no voltage to the coil with the key on, check the ignition fuse and relay. Not all vehicles have an ignition relay, but if your car does, you can use my relay tips to interrogate the relay socket. In these designs, the command signal from the ignition switch may be negative or positive. If you aren't sure, see if you can get the wiring diagram for the circuit. If the command signal is not getting to the socket, your ignition switch or ignition wire from the switch are bad. If the command signal is getting to the socket but the relay is not clicking, replace the relay.

Assuming now you have power to the coil but no fire, either the coil is bad or the ignition module is not sending the timing signal to the coil. You can test the coil with an ohmmeter if you have the specifications for your coil. Resistances for the primary winding vary from less than one ohm to over a thousand ohms for some coils. If you have more than one coil, check them all. This is a good way to isolate and identify individual coils for replacement. Ignition modules are beyond the scope of this tip, but I can provide a few ideas on where to start. It is a good idea to extract any and all fault codes indicated by the "check engine" light when you are not getting a spark from a powered coil. Please see my tip on fault codes.

Use the fault codes to further troubleshoot the ignition system. It is advisable to get the wiring diagrams for your ignition system to troubleshoot. If you have a fault code relating to the crankshaft sensor, this fault may prevent the computer from timing the spark. Check the wiring and connector to the sensor and make sure the sensor is tightly installed.
Most modern cars have an engine or powertrain control computer/module to send signals to the ignition coils and fuel injectors. If you have an oscilloscope or other meter that can sense a waveform, use it to check the signal to the negative coil terminal(s). If the signals are not rectangular and periodic, suspect your ECM/PCM is bad or is getting bad data from the crankshaft sensor. Knock sensors may, in some cases, also affect the computer output, though these are generally used only to change the ignition timing while the engine is running with a knock.

If your car is a bit older, it may just have a distributor with a pickup coil and ignition modulator to generate the signals to the coil. In these systems, the modulator charges the coil and then cuts the charge signal when it receives a blip from the pickup coil in the distributor, thereby releasing the spark. The spark then travels from the coil to the distributor and is routed to the appropriate ignition coil via the rotor. The signal to the coil should still be rectangular, and if not, suspect the modulator is bad.


Firing Order Help

OK, you have a distributor or unmarked coil pack and you just finished replacing the ignition wires or spark plugs. Now you aren't sure which wire goes to which plug. Or maybe you thought you got it right, but the car doesn't start. You could get online and Google the firing order, but that may not be sufficient to wire up the engine. For example, you may not know which position on the distributor is #1, or which way the rotor rotates, or you may not know which cylinders are which on your engine.

Here are some tips for addressing your concerns.

1. Look for stickers in the engine compartment that have this information.
2. Look on the intake manifold for numbers on the intake ports for each cylinder and also for the firing order.
3. Look online for information about your engine. has most of this info for most engines under the tune-up and specifications links.
4. There are some standard cylinder numbering schemes that can help. Obviously an inline engine always numbers cylinders sequentially from front to back. For V-engines, Ford goes sequentially on the right back, then the left back. GM goes left-right-left-right, like lacing a shoe. I'm sure there are more, but I'm not trying to cover them all in this tip.
5. Finally, when the distributor doesn't have #1 marked on it, how do you get started with the wires?
If the #1 piston is at TDC (you can know this by aligning an ignition timing mark or by taking the plug out and rotating the crankshaft until you feel the piston top out), it is either completing the exhaust or the compression stroke. If you can easily peek at the camshaft timing markings, you would know right away which it is. But there's an easier way to figure it out. With the #1 spark plug out and the engine cold, put your thumb over the plug hole while someone bumps the engine with the key. When the piston is on the compression stroke, it will push your thumb off the hole. Once you know you are on the compression stroke, you can turn the engine by the crankshaft bolt until it reaches TDC as determined by the ignition timing marks or by sticking a screwdriver in the hole. Once you are at TDC, the rotor will point to the terminal that you need to connect to cylinder #1. Then just follow the distributor rotation and firing order to complete the rest of the wire connections.


Engine Overheats--Where's My Thermostat?

So your car has been overheating and you've been told to try changing your thermostat, but you don't know where it is. Let me say first that this advice is usually given because thermostat replacement is an inexpensive repair that you can do yourself. Few of us that give such advice can guarantee that this repair will solve your problem, but it's worth a try.

I want to give you some words of wisdom here, but for those that just want the bottom line, let's get it over with:
The thermostat is usually mounted on the engine near the front top end, and it is usually at the other end of the upper radiator hose. So follow that upper hose to the engine, and you most likely will see at the end a small housing that is attached to the engine with 2 or 3 bolts. The elusive thermostat lies within that housing. There are a few engines where this isn't true. In those cases, look around the engine for a housing that is a few inches across and has smaller hoses attached.

Removal and replacement procedure:
Tools needed are a socket set, a screwdriver, pliers, and a gasket or paint scraper.
Materials needed are a new thermostat (preferably of the operating temperature that is recommended for your car), a matching gasket (may extend beyond the area needed but must cover the mating surface), and a tube of gasket sealer.

Most professional manuals will advise you to drain the coolant from the radiator and engine. Fine, that's good, but I don't do that. If you want to, there's usually a drain port we call the petcock at the base of the radiator. Some petcocks are reverse threaded, so be careful not to break it off if you turn it the wrong direction. Drain the coolant into a pan that can hold at least 2 or 3 gallons. If the coolant is relatively new, it can be reused. Keep the coolant away from pets, as it tastes good but is poisonous.

If you have not drained the coolant from the car, place a drain pan under the car below the thermostat.

Now remove the radiator hose from the thermostat housing. It may have a screw clamp or a spring clamp. Loosen the clamp and slide it down the hose a few inches. Loosen the hose from the housing by twisting and then pull it off the housing. Coolant may drain into the drain pan. Some engines may also have a second smaller hose attached to the housing, and there may be a sensor on it as well. Disconnect any additional hoses and connectors, but do not remove any sensor, as this is not necessary.

There may be other accessories blocking your access to the bolts that hold the housing to the engine. You will have to remove any parts that are blocking your access, but I cannot cover all of the possibilities here.

Assuming you now can access the bolts, remove the bolts holding the housing to the engine. The housing may now come loose or you may have to pry it a bit. If you pry, be careful not to damage the mating surfaces.

Remove the housing and thermostat and clean the old gasket material from the mating surfaces on the housing and the engine using a scraper.

Insert the new thermostat into the engine with the copper end first and the pointy end sticking out. Some cars also require the little hole in the disk to be on top.

Coat both mating surfaces with gasket sealer and stick the gasket on one or the other.

Grab a bolt and mate the housing to the engine, screwing the bolt in to hold it. Screw in the other bolts by hand, making sure they pass thru the holes in the gasket.

Tighten the bolts. The torque may be different for every engine, and most of you will not have a torque wrench anyway, so just get them in tight but not so tight as to snap them or strip the threads. If you use a 1/4" socket set and turn it hard, you should have it about right.

Reattach the radiator hose and any other hoses or connectors you took off.
Replace any other parts that you had to remove to gain access to the thermostat housing.
Refill the radiator with the recommended coolant for your car. Use the port on the radiator, if it has one, then fill the reservoir to the cold mark.
Start the car and check for leaks around the housing and hoses.

Allow the car to idle up to operating temperature and keep the radiator full as air bubbles out of the system. If the system has bleeder ports (common on Hondas and Toyotas) along the coolant hoses or on the thermostat housing, open the ports and allow air out until only coolant bleeds out. Make sure the engine is at operating temperature before you declare it to be fully bled of air, then fill the coolant reservoir and cap the radiator.

Don't pat yourself on the back yet. Check the operating temperature of the old thermostat and compare it to the new one. If it is different, expect your gage to settle on a new point compared to where it "lived" before your overheating troubles started. You may also want to boil the old thermostat for curiosity purposes to see if it was really bad or if it opens as designed. If it does, your woes are not likely over. If it doesn't open in boiling water, you may be in the clear. Either way, I recommend a few trips around the neighborhood to see how the gage behaves. If it behaves well, check the heater too. If both behave well, grab a cold one and call it a night.

If it is still overheating, have a seat and finish reading my tip.
So now you have to consider some other possible reasons your car is overheating. Here are the ones I've seen over the years:
1. Leaks
2. Bad fan or fan circuit
3. Bad water pump
4. Clogged radiator
5. Blown head gasket or cracked head (or block)

Let's troubleshoot these one at a time.
1. If your car has been losing coolant, you know you have a leak. If it isn't leaking out the bottom, it may be going into the oil pan or into the combustion chambers, but let's leave that horrible possibility for last. Some common leaks are the water pump weep hole (small hole at pump shaft bushing that leaks when bushing wears out), radiator hoses, other coolant hoses, radiator, heater core, and my personal favorite--rotten freeze plugs. If you have any of these leaks, your car will habitually be running on less coolant than it is designed for, and the coolant will boil at a lower temperature because of reduced system pressure. I'm not going to cover how to repair all of these but rather ask you to get back to me if you need help with them.

2. If your electric fan(s) is not coming on when the engine is hot, first check the fuse, usually in the fuse box under the hood. Then, with the engine hot and running, pull out the fan relay (usually in the same box as the fuse). If it's working, it should click when removed and again when replaced in its socket. If it doesn't, suspect the relay or sensor has failed. See my notes on how to troubleshoot the relay socket. If your gage runs off the same sensor and works, it's probably fine. If you're good with electronics, you can also test the sensor. If these are all good, either the wire to the fan is bad or the fan itself is bad. You can test the wire for voltage with a test light hooked to the fan connector, and you can test the fan by hotwiring it to the battery.

3. As I have already mentioned, the water pump bushing can fail. If it is leaking or if the belt comes off because the pulley wobbles, replace the pump. Some water pumps (notably Honda and many Toyotas), are located behind the timing cover and are difficult to observe. Fortunately, these are generally also more reliable. The other way in which a water pump can typically fail is by broken/eroded impellers. This is rare in the case of steel impellers and most common with plastic impellers. If you know what kind you have, you can use that as a factor in deciding whether or not you want to replace it. Here are some troubleshooting steps you can also take: assuming the engine is warm and the thermostat has opened, and if you can see in the radiator through the filler cap (be careful opening the cap with the engine hot), you may be able to see the coolant flowrate. If you can't see into the radiator, try squeezing (with oven mitts on) the upper radiator hose to see if you can feel/hear the coolant flowrate. A good flowrate indicates your water pump is working and your radiator is not clogged.

4. If you have a poor flowrate, and assuming your thermostat is opening, it could be caused by the water pump or a clogged radiator. If you can see extensive deposits inside the radiator, either backflush it, have it cleaned professionally, or replace it. Otherwise, the water pump is your problem.

5. If none of the above is the cause of overheating, we must consider some more serious causes. A blown head gasket or cracked head/block can allow oil into the coolant or combustion gases into the cooling system (among other things that do not cause overheating). This latter case can cause the engine to overheat within a few minutes. If your car overheats this quickly, a blown head gasket is likely (but I would still advise someone to check the thermostat before pulling a head). This condition can be verified by removing the radiator cap and running the engine until hot. Bubbles of combustion products will be seen coming up in the radiator or into the coolant reservoir. As mentioned under bleeding after thermostat replacement, it is normal to have air come out during bleeding of the system, but if the bubbles continue indefinitely, you are getting hot combustion products in the coolant.

Oil in the coolant can also cause overheating as the oil mixes and thickens or "foams" the coolant until it cannot flow or transfer heat sufficiently. This contamination is easy to observe.

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