Ok here is the story. I have an '86 TA but swapped on an '89 TPI system. The throttle body is a '89 style BBk 52 mm, but the coolant passage that bolts to the bottom of that is from the '86 stuff.

It either hunts for an idle like you wouldn't believe, or stays stuck at pretty much one rpm range. It doesn't try to idle where the computer tells it too. If I reset the minimum air and TPS it does the same thing but would eventually settle around 500-600 rpm.

So I figure it is most likely the IAC motor. Before I go buy a new one I check on the part numbers at autozone.com. They are different for both years. Any ideas on which one to buy or whats wrong with my car? From what I remember the throttle bodies have the same openings for the IAC housing. Also, I am using the .bin file from an '89 corvette since they came with a 350 and manual tranny.

 

I'd try cleaning the IAC before replacing it. I had idle problems too but were gone once I cleaned the pintle and put it back in. Now I have a rock solid idle.

 

89+ throttle bodies had a different IAC setup. I can't remember the specific setup on the 89+, but I know that the plenum doesn't have the IAC hole like the older ones. I believe that it either just opens the throttle blades, or it routes back into the airstream within the throttle body. Either way, it's quite possible that the older IAC assembly won't be compatible with the newer TB.

Sorry about shooting from the hip here. I usually only post if I know what the hell I'm talking about, but since nobody mentioned the TB differences yet, I felt that I could at least contribute that much.

 

Jim85IROC, I have the whole TB/plenum situation under control. But for the record, the 85-88 plenums have a triangular hole between the throttle blades which matches a hole in the TB. That hole is part of an 'idle runner' that goes under the plenum and down to the intake by the cold start injector. These earlier setups also have another small runner on the passenger side that works part of the EGR I believe. The '89 and up models do not have this 'idle runner' (but they do have the EGR), instead the TB has 2 rectangular notches behind the throttle blades that simply dumps the air into the plenum through the regular throttle blade openings. Both TBs have some sort of hole in front of the blades that drops down to the IAC motor housing, then that passage goes back up to the TB. Also the TBs have different throttle cable brackets. To me it looks like the tranny and cruise control points are the same, but the throttle is different. The earlier ones have a standard looking stud and clip design where the newer ones have a 'rocking chair leg' that the cable sits in. You can swap cables and keep the bracket that bolts to the plenum to make it work.

But that is where my real question exists. Are the coolant passage/IAC housings the same for all the years? If not I have to get a newer one, but all the bolts line right up so go figure!!

86 IROCZ28, thanks for the idea. Use carb cleaner on that right?

 

I have the 89-92 52 mm bbk on my 88, I have had problems with idle from time to time but, it seems to be more of a 02 problem for me it goes to open loop and acts like garbage, but, most of the time it works fine. I switched the cable for the throttle to an 89 style that is all you will need to do. as for the passage I have no Idea it never occured to me but, makes sense. you could try making your own gasket with out that hole and see what happens. my passage may just be cloged.

 

Yeah just spray some carbie cleaner on it and it should at least clean it out a bit.