starting points for jetta problems

[sharpshooter33 at adelphia.net (David Brown)]

Ok, I'm at a loss on this one and I'm just wondering if anyone has a start point on testing and figuring out what problem(s) I have.

The 86 Jetta was running fine for 2 weeks.  Then on my way home from work....about 10-20miles in the car starts missing real bad.  It has smoke coming from some place in the upper exhaust back up into the motor area.  I was aware that the exhaust was loud, but with the missing it's not emitting smoke, (definite exhaust smoke) back up into the engine area.  Smells rich also.  It has a pulsing idle.  rev'ing it up you can get it home, but it still is missing even at higher rpm.  I changes the plugs, and tested the O2 sensor by unplugging it and still same idle.

I also found that if I put pressure on the Hall plug it would die.  I found that the distributor cap was on backward and not locked in properly, but it's new and I checked it out moved the plug wires around and put it back on properly.  The pressure on the hall unit doesn't cause any idle changes now, but I still have the same missing problem.

My thoughts are electrical....coil or some signal problem to the DPR that's making the mixture to rich?

Any thoughts on were to start or things to check LMK
Thanks

David 
86 16v rocc turbo
86 16v rocc front damage waiting on face lift
84 8v rocc wolfsburg - organ donor
86 8v Jetta GLI - Ungrateful daily driver (maybe)