I have been having a stumble/miss for a while now. Swaped out ECM's today with no luck. Although the cap, rotor, wires and plugs are new I decided to pull individual wires from the cap to see what happens. After pulling a couple of wires I noticed sparks comming from the coil wire where it connects to the coil. This stumbling is cyclic in nature. You notice it while driving as well as when idleing(Except when car is cold). One thing I noticed though is when #7 was pulled the stumble became regular and did not cycle(maybe #7 plug or wire is bad). The sparks comming from the coil have me concerned, I don't think this is normal.The car has given me a code 42 and code 43 in the last few days. No codes with the new ECM.Ignition module? knock censor? I don't have a volt meter to check any of this stuff. My head hurts, I need to stay away from this car for a few days!

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1990 Iroc convertible,305 tpi,Black with black leather interior,lowered,Taylor 8mm wires,K&N's

 

When you disconnect a wire, the spark has to go somewhere...
It may be that you have a weak/damaged wire, or maybe a bad ground.