Weird problem. Starts good. Idle stable when cold. After it reaches operating temperature it changes rpm 1000 rpm down to 600 rpm and back again.

Replaced the idle air solenoid and O2 sensor perhaps a slight difference.

Not the power brake can. I isolated the power brake canister and it made no difference.

While the engine is in the irregular idle stage I disconnected the idle air solenoid and it killed the engine.
Plugged it back in and restarted. Engine idle correctly.

Any help is greatly appreciated.

 

I would check your temp sensor and or the crank sensor. Sounds like the computer is getting the wrong information.

 

Can we get a little more info ?
Auto trans, std trans ?
Does your vehicle have central fuel injection or injectors for each cyl ? (sequential injection)
The solenoid you replaced, did it have a on/off switch on the tip of the solenoid ?
This goes back a bit and need to know these things before offering any suggestions, thanks.