After recently installing my new trans and stall I have come upon a tuning issue that wasnt there before. When the car hot starts it seems (havent let it cool) it revs to 1600rpm and hangs there for a few seconds. The iac counts settle down quickly to about 60 so it revs at the programmed idle of 925 in park. All other iac appears to be working fine and the motor is functional. There are no other driving issues just the startup.

I am wondering if i can command less iac counts on hot start. So far the cold start works perfectly, car fires up right away to 1000rpm.

Looking for either tuning fixes or tweaks for the throttle position. Airflow is about 9-11g/sec in park or in gear which is about what i see on everything after its settled down to idle. Vacuum seems to be correct and improved with the stall. The only thing I have done to the tune is lean out the hot open loop sections for hotter coolant temps, wideband now shows 14.5 a/f at hot idle during open loop, before it was about 13. Not sure thats part of it or not just throwing out whats been done.

This isnt really a huge issue its just kind of when a car with full exhaust and a loud cam fires up and idles at 1600 rpm for a couple of seconds. Too much noise and it annoys me.

Appreciate any help fellas.

 

I have a '94 odb1 and there is a table called "IAC park position Vs. coolant temperature " that is used for initial startup. Should be something similar for your '96. Also "Idle overspeed spark retard Vs. RPM" table could slow it down faster. Again these are ODB1 tables..

 

I have an obd1 conversion, guess I should have said so.

I have tried the iac park position vs. coolant temp, to no real effect (I have returned this to stock). My understanding of that table is that it runs down quickly from 160 to that number. For startup the iac is always at 160 steps regaurdless for me. I also have a very agressive retard system in place for too high of an idle. When I ran with the stock stall it would do this when I took it from drive to park, taking 10* of timing out on the higher end of that table stopped this cold.

I'm going to try a few things today and see what I can come up with. If I figure it out I will post back. Keep the suggestions coming, maybe i'm just looking over it. I have tuned alot of cars, just never had this particular issue. I thought maybe it was a vacuum leak, but after spending all day on it yesterday with some starting fluid and moving hoses around damned if I can find it if there is one. Plus the idle airflow looks right so that rules it out too.

 

Alright I figured it out. My closed tps spark advance was 34 in the 1600 rpm range. Lowering this to 27 like it is from 400-1200 fixed the problem. I guess idle overspeed retard doesnt kick in for a few seconds until the idle has stabilized to the desired level.

As an aside it apprears that the steps in park vs coolant temp do have an effect, the lower these values are the faster the iac will shut down or at least thats what I am seeing on my car.

I have messed with this a few different ways this morning and now when the car starts hot it just immediately jumps to the desired idle rpm and stays rock solid there. In effect the timing advancing at idle is alot like a secondary iac system, which is how pcm uses it with over/underspeed retard/advance tables.