Ok, I just got my car back after a rebuild, and it pulls really hard and all, but just cruising, there is a stumble sort of feeling. A surging of sorts. First things to check will be plugs and wires, but could a bad coil do something like this? I'm just hoping to narrow it down to something before I replace the Opti unneccessarily. Any thoughts would be appreciated. Thanks.
Dan

 

Usually a something like a coil going away would be more noticeable under load, not at cruising. That does not rule it out, though. Check wires and obvious stuff, first.

 

stumbling, check for any intake leaks

 

Do you have an M6 or an A4?? Could it be a little cam surge? A timing issue?

 

It's a manual. We checked for vaccuum leaks this evening, and didn't find anything. I don't think it's a timing issue, because it picks up great and pulls when you get on it. The exhaust smells rich to me too, which makes me think there is a misfire. I don't think my coil has ever been replaced in 213,000 miles or so, and I just wanted to see if those could be the source of the problem.
Dan

 

You said you had just gotten the car back. What did you have done to it?

Does it idle ok?

Can you get the symptoms to change by changing throttle position?

You could try looking for sparks under hood at night; but if you can’t get the problem to reproduce while parked, I don’t think it would be conclusive.

 

Usually when a coil goes bad it goes and you can tell right away from my experiences w/coils - but I could be wrong.

What all was done to the car during the rebuild?

 

The rebuild took it from a normal Z28 with 212,000 miles to a new 396 stroker with new heads and cam, headers, etc.
Dan

 

Glitch in the fuel map maybe?

If it idles good, it probably isn't a vac leak.

When my opti went out, it stumbled on light throttle, and cleared as RPM increased.

If you down shift and cruse at a higher RPM, does it still stumble?