Skip the auto shop - Our mechanics make house calls

Q: RPM fluctuates

asked by on

When I start my truck it's loud like a fan is on before it settles down. No matter if its warmed up or not. When I turn my heater on the RPMs fluctuate as high as 1200 and back to about 500. Just does it back to back non stop as long as heater is on. I'm also able to notice the difference when driving at low speeds. When it fluctuates the car speeds up. When I turn the heater completely off it doesn't do any of that. No fluctuations even when in idle.

My car has 177000 miles.
My car has an automatic transmission.

With the age and mileage of your vehicle, it would probably benefit from a throttle body service including cleaning the idle air control valve. Over time, oil and carbon build up on the throttle blade so it does not sit perfectly flush in the throttle body bore. This effects the throttle position readings to the ecu.

Also due to carbon build up, the idle air control motor/valve passages will get clogged up, reducing the size of the air passage as well as slowing it’s movement. The idle air valve will let more air into the engine at idle when the heat-A/C is turned on because of the added drag on the engine.

If the idle air valve is clogged with carbon or not moving properly because of it, you can get a low/shaky idle, surging and even stalling when the heat or A/C are turned on.

If you’d like to get this fixed, consider YourMechanic, as one of our mobile technicians can clean your throttle body and service your idle control valve if necessary.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Bad idle air control valve

Hi there. I would need to know what the codes are to know if they are related. The idle control valve failing can cause other codes to come up, but there are other problems and codes that can come up...

Q: Abs and brake light on

Hello. The most common cause of this is low braking pressure. Start by checking the brake fluid. If it is low, then it can cause this. If the brake fluid is fine then the electronic brake control module must be...

Q: Leaking clear liquid

Hello. Leaks that expel clear fluid can come from a few different sources. If the vehicle already has known transmission issues, it may be possible that the leak is related to the transmission, even if the fluid that is leaking...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...