First never had a problem with it vibrating or shaking after we put in a intake manifold gaskets because it was leaking a bit of oil. Also the spark plugs have oil. The muffler sounds muffled like it can't breath. I want to know what are the causes Thanks
My car has 170000 miles.
My car has an automatic transmission.
Oil leaking down into the spark plug wells can causes the plugs to short out to the cylinder head, yielding the misfire you are experiencing. Replacing your valve cover gaskets, the plugs, and cleaning out the spark plug wells, and the rubber boots from the plug wires should resolve this problem. If you’d like, a YourMechanic certified technician can come to your location to perform one or both of the following recommended services on your vehicle:
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