Maybe you can shed some light on this because I know other board members have experienced it. I have made a post about it already but nobody seemed to know why but many complained about having it. After my blower/obdI computer swap when I start my car it goes up to about 1250 or 1300 rpm on my autometer tach and then slowly comes down to normal 800-900 idle depending on how hot it is. Why did it just start doing that because of an OBDI swap? I had some kind of idea that it may be the IAC. Is there any way to check or anything in lt1 edit that can fix it? Thanks again fred.

 

I've seen this subject in other threads, and there isn't much I can say about it. I'm not all that knowledgable in the blower setups. And I can't think of any reason that OBD-I would respond differently than OBD-II.

It is normal for the idle speed to be elevated at low coolant temperatures... the table of idle speed vs. coolant temps is in my ScanMaster writeup. Did it not start cold at higher idle speeds before?

Maybe there is some subtle difference in the way the OBD-I and OBD-II PCM's handle the "learned IAC counts"..... the initial postion the IAC motor assumes to control idle, based on recent experience. Maybe there are differences in the way you program the initial IAC position?

Also, the PCM will normally elevate idle speed if the TPS sensor is not showing 0% TPP. Is it possible that the blower is holding the blades open a fraction of an inch, because of the small amount of boost that is present at idle?

Don't know a lot of the details, and its been more than 3 years since I have stopped using the stock PCM - at least for anything other than VSS and IAC.

 

You should contact your tuner and ask about what changes have been made to the idle tables. My guess is that the idle was raised intentionally to help the car deal better with the cam when the engine is cold.

 

You can adjust the IAC for different coolant temperatures on startup. This will adjust how the car idles on initial startup and it will gradually scale down until you reach the desired idle at the pre-specified coolant temp.

 

Thanks for the responses guys. I will contact Brian about changing the initial IAC value with respect to coolant temp. Something Fred said got me thinking... if the bypass valve was not working correctly would it do what I described? I have had freescan running when I start the car and the IAC starts high and then gradually comes down so I'm pretty sure it's the IAC. I am going to ask Brian what he did with my idle tables... The car would maybe go to 1100 or 1150 before the blower and then come down to 8 or 9 hundred after it warmed up.