Something German S550, 69 Eldorado, 68 Impala, If I tell you the rest, well
How's the plenum gasket between the intake and throttle body(Rubber Boot). See if it has a crack that might be your problem.
Just guessed on which one. Started with the grey one because it's the easiest to remove. Luckily for me that was the one that had a bad coil.So how did you know which one it was? I have replaced both my coil packs in the last three years. Simple to do, but did you just guess it was the front?