My 84 has long suffered from an intermittant rough, stumbling idle condition.

Finally I waited it out on a day when it seemed consistently poor, and Ian put it on the scope. He has the best instruments in town, he is proud to point out.

Sure enough, just like an EKG the problem manifested as a collapsing ignition pulse.

After some investigation, it's source was traced to a faulty secondary (booster) coil, the one with no high tension lead, in front of the radiator on HE cars.

Funny thing, while waiting for the new part to arrive I've been running the car with just the one coil--the secondary one is simply a parallel inductor used to "boost spark voltage" as part of the lean-burn HE makeover in 1981--and the car is running aces better with just the one coil!

Must mean the secondary one has been leaking current to ground for a long time. It's original to the car, I'm certain.