Jumped timing?

I have an '86 Iroc with LG4, edelbrock performer, Holley street avenger, Accel non-computer distributor, hooker headers. With the timing set at 8 btdc I can't get the engine to idle at less than 1200 rpm. I've tried adjusting the timing both advanced and retatreded with no success. Could this be caused by the timing chain junping timing? If not why else can't I set my idle any lower without the engine stalling?

If the car starts, runs smooth and revs. from 1200rpm. It probably is not timing. In most chases this is caused by vacuum leaks and carb. tuning.