My customers have a 2004 Porsche Cayenne S, recently the engine feels like it's skipping when my customers is driving between the speeds of 25-50 mph. When my customers is in low gears, driving less than 20 mph, it's fine, and when my customers is cruising in high gears, it's also fine. It's mostly when my customers is accelerating at mid level speeds. Additionally, my gas mileage in the city has been only 9-10 mpg. Is this a faulty spark plug? my customers just bought the car a few weeks ago, so my customers don't know if that gas mileage is poorer than usual Launch X431 V. my customers 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 my customers fueled up, my customers did not use premium gas, my customers don't know if that is relevant or not. Please shoot me any insight you have, my customers would like to hear a mechanics opinions - thanks.