My Gen 3 has had an intermittent problem for a while with misfiring/stumbling. The dealer took a look at it twice, and replaced all the spark plugs one time and the driver's side front O2 sensor the second time. Over the winter, I replaced the ignition wires with AB Wires, and the coils with Screaming Demon. The problem persists. It is hard to nail down precise conditions that cause it, but it does seem to get worse the hotter the engine gets. It was particularly bad today, and on one occasion when it was doing it while idling, I could smell rotten eggs, so I presume I was getting fuel but no spark.

The car judders badly when it happens, but then smooths out for a few minutes before it happens again. It happens in all gears, at any speed. The car just appears to run out of power when it happens; you can't accelerate.

At this point it has new wires and coils, recent (1,000 miles) plugs, and a new O2 sensor. I checked the plugs and injectors when changing the wires, and they appeared ok. I've cleaned the throttle body. No check engine light is being thrown. The car is totally stock aside from the new wires and coils.

I don't want to take it back to the dealer, they've already had two cracks at it, and it feels like throwing money away to take it back again. I'd appreciate any hints as to the next place to look, or if people solved similar problems. I searched the forum but didn't find anything yet.

Thanks,
Paul.