Skip the auto shop - Our mechanics make house calls

Q: Crazy idle

asked by on

I just got this car and the owner said he replaced the throttle body on it and when you start it the idle will be normal until the temp goes up and then it will go up then back down then jump up and go back down and continues doing that until you put it in gear then while driving if you push the gas to fast it will start surging and no power when you hit the gas you have to let off of it for a minute and then works again what would cause all that

My car has 137000 miles.

Hi There, It sounds like you may have a dirty or failing idle air control valve. The idle air control valve monitors 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 and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about ~800 RPM, 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 inspect your vehicle.

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: Abs light, Trac light, service vehicle light on, brake pedal sinks to floor hard to stop vehicle

During the service of these components, the brake hose bolted to the caliper is not required to be removed. If it was removed and the brake system was not bled properly, air trapped in the system can cause your symptoms....

Q: 2007 Nissan Frontier won't go into any gear

The shifter cable connects the interior gear selector to the transmission. This allows the driver to select the correct gear. If the cable is detached, the gear selector will just flop around but not select any gear, as you describe....

Q: Cost of a leaky engine valve

Hello. If the estimate to repair a leaking valve is $300 then that is much too low. It is common for this engine to have valve problems but it can cost between $2000-3000 to fix correctly. This requires that the...

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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...