I'm having an issue with bad stumbling and misfiring under load. The car was running fine until a day ago. It mainly happens when pulling away from a stop, between 1k - 2k, and above 4K. It also doesn't idle smoothly, jumping a couple hundred RPM every couple seconds, though I'm not sure if this is related or if it needs a tune due to the full exhaust.

Couple things I tried:

• Disconnecting O2 sensor didn't make a difference.
• Disconnected ignition modules. Car starts on primary but won't on secondary. Car keeps running if secondary is disconnected, dies if primary is disconnected.
• Thought it might be the distributor belt. Didn't want to strip the screws so tried an alternate test. Plugged the primary coil wire into the secondary distributor and left the secondary ignition unplugged. Car starts and idles fine. It seemed to idle smoother with no jumps.

So it seems to me the secondary coil may be bad. Does this seem correct and would it cause the symptoms above? The coils are black so I assume they are the stock ones.

 

 

Time to convert to the 993 setup. Black coils cannot be found, and the new silver ones cannot be trusted.