Hello all! Here is a new one for you. I need idle problems experts. Well, it never happend before to my car but for the last three or four days i've been having some fluctuating idle problems when i first start the car.
Here is what happens: I start the engine, (regardless if it's cold outside or not) and just like every normal cold engine the idle at first is at the 800-1000 rpm range. It's there only for the first 10 seconds and then i starts to move up and down. It goes up to 1400rpm and then goes down to 800, then again it goes slowly up and down. This repeats for ONLY 2-3 minutes OR until i rev the engine a few times to 2k+ rpm. After this, my idle is back to normal for the rest of the day. If i park the car for more than few hours and i start it again - the same thing repeats for the first 2 minutes or less.
This started to happen right after i replaced my accessory belts few days ago. I don't know if they can be related to it.
What should i look for since it is not a constant problem that appears the whole time???
My fuel filter is 20-25k miles old, my spark plugs are BOSCH 4+ (50k miles old), my air filter is almost new, i run Techtron Fuel system cleaner every 5k miles... There is no loss of power or weird noises.
2 years ago, my mechanic told me that my Idle Trotle switch is bad. I don't know why he said it because i really never had any problems with idle and etc. I never replaced that switch and i never had a problem until this week.
Could the reason for my problem now be this switch??

This is the 10V 2.3L engine with 155k miles on it.

Thanks for any help!

 

So any time you start the car again when the engine is already warmed up, you will get a normal idle; just on a cold start the idle fluxuates.
I would suspect the thermo sensor switch, just forward of #1 spark plug, the sensor with the two leads, it may be malfunctioning when it's cold and sending an erratic signal to the idle control unit. or just maybe the leads are not making good contact.