I've been doing work on my idle system and have things working pretty well. However, I don't understand the relation between the cooling fan system and the idle control system.

After starting it cold and letting it heat up, the engine happily idles at around 750 and I can turn on/off electrical loads & A/C and see the Idle Air Control Valve make the appropriate adjustment to the idle RPM. When it idles for a while such that the coolant temperature rises and the cooling fan kicks in, I see the idle RPM go up to about 900 (which I would expect to happen). However, when the fan turns off, I would expect to see the idle RPM go back to 750, but instead it stays at 900. When I turn off the engine for about 5 minutes and start it back up, the idle RPM is (correctly) at 750.

Is this normal behavior? I looked through the shop manual and can't find any reference to cooling fans and the idle control system.

Thanks for any help!

 

My question is, did you turn off your AC? If you're AC is still on, and even the fan is off, your idle should be kicked at 900rpm to keep it running properly, otherwise it will bog and the engine will feel like it idle rough.

-AzEKnightz

 

Yes, A/C and all other loads were off.