1979 242, lambda sond, b21f engine. car was given to my gf and it is in great shape, it has been very reliable, when she got it I notices a vibration at low rpms. later I replaces the UV joint closest to the nose cone of the Automatic tranny to fix the problem. I have replaced the o2 sensor, fuel filter,plugs, wires, rotor,cap primary coil, alternator brushes, steering rack, in-tank pump,main in-line 12v pump,fuel filter, a couple vacuum lines, change the oil/filter on reg basis. It has a miss under load, a hesitation that is stumping me. I checked the timing for the first time yesterday and it was at 20deg btdc!! I retarded it back to 8btdc (what the sticker says under hood) when I check the timing the mark does not do anything when I pull off the vacuum line off the advance capsule, could it be frozen in the advance state? i'm almost out of adjustability on the throttle/idle adjustment screw, that is why I question that. I think the next thing for me to replace is the reluctor and pick-up coil in the dist. what about the ignition control module? could that be bad? I always thought those were working or not, no inbetween. I have the hanes service manual so I have schematics. I want to completely rule out ignition before I go into the realm of fuel injection. thanks in advance for your help!

I will guess that your fuel regulator is bad-check your fuel pressure-the mixture is bad because you have the throttle so open to make it idle. If it stalls easily when engaging gear or stopping, then it's going to be rich-soft black soot in exhaust tailpipe, petrolly smells at rear of car after warmup. If just weak running, it's lean. over advancing is caused by rich mixtures not igniting well, have you checked your air filter element? any air leaks in the intake plumbing (remove concertina hose to check it), is your oil trap/flame trap blocked? Do check your valve clearances, they can get too small if unattended. is your idle air valve working, is your rich start injector working/leaking? Does your throttle linkage have excess play? any old/cracked vacuum hoses? Is your fuel vapour cannister still ok, and properly connected?

The injector on the cylinder that is missing may be partially plugged or have a poor spray pattern. You can check the spray pattern by removing the injector, and with it hooked up to the injector hose and its tip in a jar to catch the fuel, turn key to "run" and manually open the air flow sensor vane to observe the spray pattern. The Haynes manual describes the procedure. If you get dripping or a poor spray pattern, replace the injector. Of course you could try some injector cleaner in the gas tank.