Skip the auto shop - Our mechanics make house calls

Q: Rough idle and RPM fluctuation

asked by on

truck has a very rough idle, today I replace both vct soilnoids and it did not help have a check engine is on runs better with overtime off, two years ago I have both timming chains replaced and plugs too. runs fine on the highway.

My car has 160000 miles.
My car has an automatic transmission.

This may be related to a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer which will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed. This is all controlled by the idle air control valve. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Automatic car stalls when put in gear

The internal transmission seals are leaking pressure to reverse and forward gears at the same time and lock up transmission then stalls the engine. You will need to have a pressure test on the transmission to see if the leak...

Q: Lubrication for the U-joints on a 2003 F-150

Yes. But, if you are buying new U-joints, they come pre-lubricated these days. If they don't, when you buy the joints for Ford, it'll tell you which lubricant to use. If you are buying at an auto parts store, they...

Q: Car won't start - Ford Escape

If the battery starts out at 12 volts and is dropping to 7 or 8 volts, then you have a bad battery. When cranking, it shouldn't fall below 9.6 volts. There may be other issues at hand, but the numbers...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...