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2004 Porsche Cayenne S, recently the engine feels like it's skipping when I'm driving between the speeds of 25-50 mph. When I'm in low gears, driving less than 20 mph, it's fine, and when I'm cruising in high gears, it's also fine. It's mostly when I'm accelerating at mid level speeds. Additionally, my gas mileage in the city has been only 9-10 mpg. Is this a faulty spark plug? I just bought the car a few weeks ago, so I don't know if that gas mileage is poorer than usual. I had the car at the Porsche dealership about 3 weeks ago for a PPI full inspection and they said everythig looked good at the time. Also, last time I fueled up, I did not use premium gas, I don't know if that is relevant or not. Please shoot me any insight you have, I would like to hear a mechanics opinions

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Hi Bemshawn,
Did you get this resolved yet? Sorry for late response.
Sounds like more sensitivity is needed to truly give a "good" diagnosis. It's likely you're having an ignition related problem. it may not be "fine" in all situations you describe.
You may have mis-fire that is just less noticeable at low load conditions.
Spark plugs need to be replaced at 40K intervals; all coils should have been replaced at least once in this engine. Check service records. Once you're sure spark plugs are within service window, connect to PIWIS for rough running at idle. this will allow you to identify specific cylinder(s) that may be mis-firing at idle. replace those coils on rough running cylinders. Expect to replace the remaining coils next Tuesday ( meaning within the near future).
When the ignition system is performing correctly the 'skipping' will disappear and gas mileage will improve.... to 15mpg. Using less than premium fuel makes the engine seem a little lethargic and drops the mpg. If you extend out the math you will find using less than premuim fuel saves no money. Less MPG uses more gallons, therefore about equal dollars per thousand miles driven.
Charlie
 
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