Q: Truck's rpm fluctuates and shakes when idling, engline light on code reads: cylinder 8 misfire.

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The truck's rpm fluctuates when idling, the engine light code reads cylinder 8 misfire. I have replaced the spark plugs, wires, cylinder 8 coil, and cylinder 8 fuel injector but the truck still runs rough.

My car has 106000 miles.
My car has an automatic transmission.

If spark and fuel have been eliminated as the cause, check for a vacuum leak. If there is one located near cylinder #8, it can be causing the misfire. If no vacuum leaks are detected, then a compression test is in order. There is a technical bulletin #PIP4138K from GM for this concern relating to a valve-train and/or camshaft issue. If you want to have this checked, a professional from YourMechanic can come to your car’s location to diagnose the rough idling to let you know what’s going on.

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