Hi Everyone,

87 corvette (auto), I have a bit of a surging idle/vibration at stop that I noticed today when finally getting to drive my vette around. In playing around with it today, I've noticed that on start the idle surges between 400-1000 at cold and eventually will even at around a proper 600-700 when driving around. I let the car warm up in the driveway today and the idle speed kept surging like that (roughly 500-900rpm) even around operating temp, and it would eventually tighten up around 600-700 but still drop and then surge at times. Weirdly enough, it would settle out at 600rpm when I would set the AC on for a moment and turn it back off. Other than that, the idle would eventually settle and continue to creep around 500 to 700rpm and send a fairly strong vibration through the car at moments.

The car seems to idle much better around 700-800rpm rather than the lower 500-600rpm at a stop (mainly in park, pretty similar in neutral). I have the timing set to standard 6 BTDC and adjusted the TPS to .56v at idle. I had a shop (unknown to me at the time) change out the pigtail connector on the IAC and I think they may have messed with that a bit also. Is there any benefit I would get by going through the procedure of resetting the IAC and readjusting the TPS after? I would like to try to get the idle to hang a bit higher since the car seems to operate better at 700rpm idle rather than falling toward 4 or 5 and keep surging. Or is this more or less normal that I should not care too much about?

Any suggestions for me to look at would be very appreciated. Thanks!