Answer: Try replacing the primary oxygen sensors (2). It sounds like the idle air control valve is working fine it is just getting a bad signal.

Question: 2003 Mercedes E500 mileage: 56,000. I really, really hope you can answer this one. Let me know if you need more details or if it is something that doesn't have a clear answer. My car periodically increases its idle while at the same time; the antilock brake light comes on. This behavior occurs at 10 or 15-minute intervals at times, or many times the car just idles fast with the ABS light on. Idle is as fast as 20,000 rpms. It has a new alternator and a new battery. I did notice there was no blow-by smoke seen when looking inside the breather with the motor running.

Answer:   This is a difficult problem to detect because the computer can not sense a malfunction, the vehicles computer system thinks everything is ok. In reality what is happening is the electrical component inside the MAF sensor becomes contaminated by air impurities. These containments imbed themselves to the electrical component that senses the air flow causing the sensor to be slightly off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS, depending on manufacturer. It does the same thing only with different names).

Question: 2001 Honda Civic mileage: 133,000 When I start the car when it is cold it starts ok and idles for 7 seconds than stalls. The third time I start it it stays running and idles ok. When I drive the car, it runs and idles ok. If I shut the car off when it is hot and start it back up in five minutes it idles very rough and sometimes the check engine light will come on. The computer code is 44 - lean exhaust when it is idling rough I take out for a spin and it runs ok. I had the fuel pump changed and same problem. I changed spark plugs and fuel filter 6 months ago. Any suggestions.

Answer: Try cleaning the idle speed motor and idle passages, then check for proper operation of the speed motor. Check for vacuum leaks.

Question: 2003 Dodge Truck 1500 mileage: 64,000.  This problem has happened 4 times over the last 2 weeks.  When the car is idling (like at a stop sign), something under the hood buzzes and a puff of smoke comes out.  It began as just a short buzz that repeated itself once, but the last two times the buzz has increased in length and the amount of smoke given off increases.  The smoke is gray, not black.  I had my alternator checked, and it is supposedly OK.

Answer: The buzzing sound may be caused by the cooling system overheating and the radiator cap releasing pressure.  The smoke may be caused by the escaping coolant turning to steam.

Question: 2002 Dodge Caravan mileage: 100,000.  This is what I've done to our van so far: 1.  Compression test of 150-160 (all six cylinders) 2.  Fuel pressure is good (50 psi) 3.  Timing good---mechanical and ignition 4.  Igniters---continuity check was good; Noid light check was good  5.  Idle air control valve resulted in lowering of RPM when disconnected 6.  Removed exhaust pipe, which took catalytic converter out of play--no change 7.   Replaced: O2 sensor; map sensor; plugs; wires; fuel filter; air filter.  Van still runs rough at idle, burns rich (black smoke), lacks power and stalls if driven.  Self-diagnostic shows no codes except for battery disconnect.

Answer:   Check the fuel injectors for proper spray pattern and volume. Also check the oxygen and coolant sensors.

Question: 2001 Chevy Lumina LS mileage: 70,000.  When starting engine, car cold (overnight for example irregardless of outside temp 20-60 degrees) the engine wants to rev up to 3000+ rpm and idle back down to 300 rpm or just quit altogether.  Unless you sit there and hold the rpm steady at about 2200 rpm, it will not idle at the correct rpm of 7-800 rpm.  Car has done this since we have had it at 65,000 miles.  Took to Chevy dealer last winter (cold temps mean you can’t start car and go in where it is warm and wait for it to warm up!) and they could not find anything wrong.  Replaced a hose and that is all.  Nothing electronic found to be bad.  Hope you can help with this problem.  It would be greatly appreciated!  Thought that you may have seen this problem on this engine and have a fix for it.  Thanks

Answer:  Here are some things to have checked: 1. Check coolant temperature sensor, it may be out of range;  2. Check fuel pump pressure;  3. Service and clean the idle speed control passages idle speed.

Question: 2000 VW Jetta mileage: 90,000.  When I start my car up it seems to run very rough but I have replaced a lot on the engine to try to solve this problem new plug wires, plugs, cap, new water pump, new power steering pump, new idle valve, new knock sensor, all new hoses and anti freeze, new vacuum lines, new air filter, new fuel filter, had the injectors cleaned at the dealer, new battery and new coolant temp sensor.  I have looked at the motor mounts and transmission mounts and they look worn but I really don’t know if that would cause this problem but the problem gets worse when you put it in drive the car steering shakes (car not moving) and when you give it some gas the car stops shaking.  It shakes at idle speed up to 10 on the tachometer but when you are stopped and you take it out of drive, it stops shaking or vibrating would be a better term.  The engine runs great and does not miss at all.  I have looked at the engine when put into drive and it moves about 2 inches or more when put into drive.  Can you help me diagnose this problem?

Answer:  Replace the motor mounts.  The motor mounts must be in good condition to constrain the motor from shaking.  From what you described, we believe your motor mounts are failing.

Question: 2002 Jaguar S Sedan mileage: 70,000.  The engine will not idle down. At an idle it speeds, the rpm's go up and down from 1000 to about 1500.  I have checked for vacuum leaks cannot hear any.  Sometimes the car idles OK.  I am new at working on Jaguars.  Need help.  Thanks a lot.

Answer:  Your car is equipped with a electronic throttle control. So there is no adjustment. The idle speed is determined from the ECM. You need to scan your car for trouble codes. A oxygen sensor or Mass Air Flow Sensor has probably shorted and needs replacing.

Question: 2004 Chrysler 300M mileage: 45,989.  When I come to a stop the tachometer reads about 800 rpm, within 5 seconds I can watch the tachometer drop about 150-200 rpm's.   Where else should I look?  By the way, the computer doesn't show any codes.

Answer: Try looking for engine vacuum leaks, then try replacing the mass air flow sensor.

Question: 2003 Ford Taurus mileage: 60,000.  Help!   I have a rough idling problem.  Checking things over I have discovered that there is a vacuum being supplied to the EGR at an idle.  Knowing that there should not be.  The EGR Valve Sensor and the vacuum valve that it controls have been replaced.  Upon no improvement, I bought an Actron 3 code scanner.  The first part of the KOEO test showed 111, that it passed.   The second part showed 326 (continuous memory), saying the EGR sensor has a low voltage signal.  There is no "check engine" warning light.  All vacuum lines have been checked to the best of my ability.  There also seems to be a slight overheating problem that seems to get warmer after idling for a while, but it does not overheat.  The engine temperature.  Sensor has also been replaced.  I did not continue on with the code scanner test.  I did not know how to check the timing?  I could not see the stationary pointer on the engine.  This all started a month after the head gaskets were replaced.  If you have any questions or need further in formation let me know.  Thank you for your time in my problem.  Any help would be greatly appreciated.

Answer:   Recheck the recently replaced head gaskets to make sure they are not leaking.  In addition, check the catalytic converter to see that it is not plugged or restricted.  Worse case scenario would be a cracked head.  When head gaskets fail, coolant usually enters the combustion chamber and in turn exits out the exhaust system.  The catalytic converters cannot tolerate the coolant and will fail.

Question:   2002 Mazda 6 mileage: 40,000.  My problem has some of the same characteristics as a previous question. My car has started to run rough in idle and stall at a stop, only in forward gears.  The car runs fine but shudders and stalls in forward gears with the brake on.  Thinking the problem might be a tune-up I replaced the fuel filter, plugs, pcv valve and air filter.  The transmission seems fine.  This car has automatic transmission, a/c, fuel injection but no turbo charger.  Thanks for your help.

Answer:   Check for a cracked air intake boot, as the engine moves slightly in opens the crack and causes the car to run poorly.

Question: 2001 Pontiac Grand AM mileage: 38,000.  Hello, About 2 weeks ago I went to put in gas and I put in 87 octane.  When I drove about 5 miles, the car started to have a rough idle and the check engine light started to blink, fearing it was bad gas, I let it go to empty, filled it up with super (92 octane) and put in a fuel treatment.... and it still has a rough idle, poor acceleration...and man I cant afford to take it in.   What can I look at to find a problem?   The spark plugs are good and everything appears to be fine.  But it's not....   PLEASE HELP!

Answer:  It sounds like you may have got contaminated fuel from the filling station. Drain your tank to refill with fresh fuel (from a different station). Replace your fuel filter and fuel injectors.