Hi , I recently rebuilt my head on my S2 including new valves,guides etc standard cam. It runs on 3 intermittant & i have to give it high ish revs to get to run back on 4 ??????? Ive done compression test all is ok, changed metering unit, put in new plugs, injectors,distributor,coil,leads !!! I have noticed its always number 3 cylinder??? Timing & fueling is spot on. Seems to only do if i go over bump so thinking its an electrical problem. The only thing i aint checked is the fuel pump wiring. I'm losing the will to live with this car! Can anyone help before i set fire to it!!!! cheers Leigh