1987 MC SS 305 H.O. -- Idles fast - around 1500/1700 or it will idle below normal @ around 500 or less and stall out. Replaced temp. sensor in thermo housing, thinking it would alleviate a problem with rising temp on gauge. Need to rerun codes if can find jumper wire for scanner input. Too many issues to try and pinpoint any 1 specific cause. Elevated temperature; fast/slow idle. Replaced thermostat as well, but only minimal effect on symptoms...