Engine Idle surge after warm with no load on 1990 Chevrolet Corvette

The engine idle surges until I turn on the air conditioner.. No vacuum leaks found.. what could be the problem.. THought might be head gasket, checked the block for leaks and nothing... In need of help..

Asked by for the 1990 Chevrolet Corvette
Check you ignition wires ASAP, I have replaced wires on Vettes of this era for this very problem which is a hunting or surging idle, with out any load that goes away with the A/C on.

here are some shops: