When the car warms up to normal operating temp, the idle gets funny. When I slow down to stop the idle goes very low to about 550rpm and then surges back up to 900 and stays.

Same thing when I start the car hot. Idles low for a second and then idles normally.

What is this?

 

sounds like your car may be losing oil when you come to a stop.... like the enertia from the stop throws the oil forward and the motor loses pressure.... why that would be i dont know, but i heard that was an issue with older oldsmobile motors, maybe your oil pickup is off? or the pan is dented? other than that? it could also be your idle air control valve... throttle position sensor? i cant tell you with the symptoms your describe, need more info... but try replacing your idle air control valve... does it throw a code at all? anything else acting weird?

 

A scanner would be the best way to determine what the problem is. Honestly, it sounds similar to a problem I was having a few weeks ago. Turned out that a value in the idle table was set wrong and at a certain temperature, the computer would drop the idle to 500 RPM, then try to go back to 1000 RPM where it's supposed to be. If you can, make a copy of your program and see what the idle tables are set to.

 

How would I do that? With datamaster?

I think its oil viscosity related but its just a guess.

 

I would think its the IAC tables personally.

 

So just unplug the battery and then drive normally again?

 

I would think more on the order of a tune issue. But yea, you can try resetting the computer.