Heater Control Valve: 87-92 V8 (exc 87H)Pre heater black plastic valve located on the front side of the upper engine area. This is for Tuned Port Injected. Throttle Body Injected.. an G code engines.. also.. NOT for 1987.. 1987 H code carby engines in Firebird & Camaro but OK for Corvette) Often these jamb on and cause increased heat in the cabin and the Air Conditioning has an impossible job trying to maintain any low temp.