I did searches for this question and found no answers. There is a different part number for idla air control valves (IAC) for 85-88 and 89-92 engines. Yes I know the throttle bodies had differences, but the valves appear exteriorly identical. Which makes me wonder what the difference is.
Along with that main question, does it then have an effect based upon what setup you are running, ie MAP or MAF.
I run a 85-88 style throttle body with a MAP system. Could the passage way for the IAC possibly be a different length?

 

I am wondering this exact same thing??? Dose anyone have an answer????????

 

Only thing I could ever find out is that the pinnings (ie IAC coil A/B hi/lo) appear to be identical. Also I found out that the IAC valves for LT1 and LS1 throttle bodies can be used without any real problem as long as the pinning is correct. I stopped worrying about it, but I still wonder about it....