philnln

I have been having problems with both cold and warm idle rpm hunting, will rev to 2k and then drop to 900K and repeat. Also feel rpm jumping under light cruise conditions. Under relatively mod to hard acceleration there is short duration pre-ignition not present at other times. Engine feels strong, timing set at 4BTDC, checked for obvious vac leaks, valves tick lightly when engine is hot(above normal cruise temp). O2 sensor replaced, mixture set using the duty cycle method for the Freq valve. Only obvious problem is a probable leaking diaphagm on the warm up regulator. Removed vac hose from throttle body and checked as per Probst's book and it does not hold vac. Also could this be leaking cold start injector problem? Some times it idles just fine with no hunting but this is the exception. Hunts and acts odd as above whether O2 sensor connected or not. Aux air regulator(with elec connector) opens and closes as it should. Do not have fuel pressure testing tool. Am trying to avoid dropping engine and/or buying expensive parts not needed. Driving me crazy. Thanks Phil

art

If the WUR closes too soon during warmup, this will happen, but it would go away when fully warm. My solution in the past has been to shorten the pin that closes the valve inside the WUR by a small amount (~.005") which allows it to stay open longer and eliminates the race then almost stall condition. I think there must be something else going on for it to happen when warm, or maybe if the WUR is leaking(erattically?), it will be confusing the system even when warm.