I'm helping my friend with a stalling problem on his 87 firebird. It has a 305 with a TBI setup from a 92 caprice.. The symptoms are as follows... most of the time it will drive fine.. every once in a while when driving real slow and coming to a slow stop it will just sputter and stall.. I thought it was a problem with the IAC valve so we put a new one in and the problem almost seems worse now.. is there a special procedure to installing one or do you simply screw it in and attach the plug? After it stalls it will sometimes take up to a minute to start again, it will then keep stalling. It only happens every once in a while, other times you can drive it all day and nothing.. im stumped.. any ideas?

*Notes: Fuel filter is new, good conical spray at the injectors.

 

when has he tuned it up last?