Pinto Car Club of America

My 79 has always had a momentary stumble on acceleration. Its like it takes off, stumbles and takes off again, all in a split second. The accelerator pump IS working (carb has been rebuilt in 07 or 08 but hasn't been driven a whole lot, maybe 10,000 miles).


I believe there is a large vacuum leak SOMEWHERE. but I cant tell where. I took a carb off one of my other pintos and had to unscrew the idle mixture screw almost all the way out to get it to run. Same with the old carb, idle mixture screw was way out to get it to run.


The transmission shifts fine so I dont think there is a leak in the trans modulator or line going to it. Spraying carb cleaner around the carb doesnt change anything. The only vacuum line hooked up is vac advance and of course the PCV valve. Both lines are hooked up and seem to be leak free. All extra ports are plugged and the plugs are new.


I'm tearing my hair out here. What could be wrong??

Check your egr valve for cracks in the casting and see if the diapraghm is still intact. My 78 was doing this a couple of years ago and the base of the egr valve was split in half. I just removed it and the exhaust manifold tube, and plugged the hole on the manifold with a brass plug and made a plate to cover the valve port on the base of the carb. The car runs great now!

Thats kinda what I was wondering about too. Also if the egr valve stayed open wouldnt that be the same as a vacuum leak? It would be sucking exhaust gasses instead of air but that still leans out the mixture.

Exactly. It should only be open at wide open throttle if I remember correctly.