Hey, my 305 TBI is kind of acting up again. It surges in park or neutral after it's warmed up. It doesn't do it when it's cold for some reason. It also will never do it if I have it in drive (automatic). Does anyone know what would cause it to only surge if it's in park or neutral? I'm really kind of confused. I've had surging problems before, but it always happened in both drive and park. Never just one or the other.

Oh yeah, I should add that I changed the IAC and adjusted it. I'm kind of questioning if the new one is even good or not though. It seems to do ok right after I adjust it. But then after a day or so it just seems to surge again.
Also, when I unplug the IAC, I don't really notice a difference in the way the engine runs. My SES light doesn't come on when I unplug it either. Is this normal?
Thanks.

 

My buddies 91 Z had the IAC unplugged, and surging, and no SES light. We found out he had a bad ECM. We also found out he had a blown head gasket. Check your oil for coolant just in case, but my moneys on your ECM being fried.

 

The car runs good.. Doesn't burn any oil, and there's no coolant in the oil or vice-versa.. It's just the surging problem I'm dealing with.. Which only happens when the car is warm.

So after he put in a new ECM, did it throw the SES when he would unplug the IAC?