Just curious here, I just fitted a standalone ecu and we are still getting the coldstart dialed in, it fowled a plug and was on 5, took it for a spin and would not clear, it merely lost a little speed and sounded slightly like a Subaru Imprezza, I replaced the plug and she's fine, we also got the coldstart set up a lot better.
Now we went for a drive with a load of other Porsches and afetr about 30 miles and very bumpy road it went on 5 cylinders again, turns out I hadnt clipped the coilpack connector completely home. Now this time it had an engine vibration from hell, the faulty connector was on the front of the passenger bank (right side looking from back) how can this result in a vibration when the fowled plug (middle plug same bank) merely made it drop power.

 

My WAG is there is something else going on.

Are there any active/pending diagnostic error codes?

 

Maybe the plug that was fouled was still getting some combustion?

 

Nothing else wrong it was just the coilpack connector had come off, took plug out and cleaned it and shes perfect again, just strange how a middle plug virtually didnt effect yet this one gave it a horrible vibration.

 

I once had a 1971 Monte Carlo (400 hp) and I was on a long trip and I blew a few lifters. The engine felt like it was going to explode. I pulled over and removed the valve covers to select two cylinders equally spaced in the firing order and consolidated my parts to the other 6 cylinders. Once finished, I had a perfectly running 6 cylinder - you couldn't even tell there was anything wrong. Sometimes a imbalance in the wrong place can really be a bad thing.