MinnesotaJeff

I need some ideas folks....

My 1979 will idle perfectly when in gear one moment, then suddenly it drops to 300-400 rpm and the car shutters and shakes. At the next stoplight it may or may not do it. It changes from a good idle to shaking and shuddering with no rhyme or reason.

I've rebuilt the carb, no change. I've checked the timing, adjusted the idle mix screws using a vacuum gauge, I've inspected all the vacuum lines. I just can't find anything!

One clue that makes me think it is a vacuum leak, is that when it starts shuttering with a low idle rpm, I can place my hand over the air horn and the idle picks up and smooths out. If I put my hand over it when it's idling fine, the car dies. So it must be sucking air in from somewhere intermittently...... Am I on the right path here? Any ideas what to start checking?

Thanks

doorgunner

Rookie guess: EGR valve or brake booster.....





but what do I know...LOL!