My Father has recently had this exact same problem with his 2007 Equinox. He bought it new, it now has 90,000 km (55,924 miles), and it also jerks/sputters/stutters when accelerating past 80km/h or 50mph. He has already gone to the dealer and their diagnosis was, like yourself, that a couple of cylinders were misfiring (which seems to be a common problem around the internet for these vehicles). The diagnosis alone cost about $100-150 and they wanted $850 (CAD) for replacement of the spark plugs, ignition wires, and cleaning of the fuel injector (ridiculous).
Naturally, he decided not to take the dealer's asking price for repair and took his car to the garage he frequents and got the spark plugs replaced. The day after, the same problem surfaced again.
After further research on the internet, it seems like the likely cause is the ignition wires and arcing that can occur between spark plugs. Who knows really. That being said, he has decided to return to the garage tomorrow and get the ignition wires replaced.
Regardless, it seems like you went through the same process and 'band aid' fix and it still had problems a couple of months later which is a little disconcerting. If you would be so kind, could you perhaps tell us if the 'sticky' valve solution truly fixes the problem later in the week? My Father would appreciate it greatly and in retrospect, myself as well, as our family will be taking our annual 1500km road trip to east coast for fishing and this would really be a hamper to our vacation. Not to mention if a car problem were to happen this year, it would be a second time in as little as three years that the family car broke down while driving to our fishing spot (this time, it would our new car as the previous car's transmission died completely and we had to purchase the Equinox out of desperation. Crazy story really).
Friday, April 16th, 2010 AT 9:38 PM