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I had a recent service done at the dealer (spark plugs, oil change, engine air filter, etc.) and ever since the service, the car is running slightly rough - at idle I can feel it shaking the car slightly and the car does not seem as smooth/free reving (overall, it's not running nearly as smooth as it did prior to the service).

I asked the service advisor whether the coil packs were replaced with the spark plugs, but he claimed that they never go bad on Caymans or Boxsters (he sees them typically go bad on Cayannes and sometimes 911s). He also hooked the car up to the computer and said there wasn't a fault code for a defective coil pack.

Any thoughts or advice on what could be causing this would be greatly appreciated. The car has about 20k miles on it.

Thanks in advance.
 

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I would bet at least one coil pack lead housing is cracked or has a loose/damaged wire. Coil packs, of course, can go bad as there is a lot of heat were they live, but that would be real evident.
 

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Could the lead housing be cracked (or have a damaged wire) without generating a fault code? Also, is there an easy way to determine if there is a damaged wire? Thanks for your help.
 

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Hello .. sorry to hear of your issues.

When I experience a change from good to bad, I find it's best to concentrate on the change(s) made rather than the possibility that it's something else. The simplest explanation is usually the best place to start. That being said .. the new plugs would be the most likely suspect .. broken, damaged, defective, poorly configured gap, dropped, etc. .. or as has been mentioned a simple ignition cable that is loose, replaced properly but subsequently snagged by someone's tool.

Let us know what you find.
 

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Yup, unless there is a total misfire, no code will be thrown, but there will be incomplete combustion resulting in a slight rough idle. I had this happen in my 05 Corvette-felt it in the right bank; dealer said I was just imagining it, but after I got a new lead I sorted it out. Of course, it could be a bad plug, but from what I have read on other threads, I would bet it is the lead housing. Good luck!
 
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