I had a rough idle problem with my 91 tpi 350. It smoothed out after the engine was warmed up to mormal. Tach was jumping from 300 to 1000 rpm when cold. Finally found the Proform distrubuter I installed several months ago was causing the problem. The plate on the top of the housing came loose and rotated slightly throwing the rotor out of phase. I could actually rotate the cap easily with the hold down still tight. It didn't change the timing until it was rotated enough to reach the next plug wire, then advance suddenly so far the engine would die. Hope this info can help someone else. I spent many hours finding this problem, I've never seen it before.