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Q: Car is running roughly at around 45 mph

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My van has gone 180,000 miles. It has been running roughly lately. The engine is misfiring as well. I took it to the mechanic's and he found and fixed a leak in the intake manifold. Also, he had the second cylinder replaced, as it was misfiring. However the vehicle is still running roughly around 45 mph, when I normally increase the speed. If I accelerate fast, the car doesn't run as bad though. What could be the problem?

Hello. It is possible that all of the spark plugs and spark plug wires need to be replaced in order to fix the problem on your Plymouth Grand Voyager. Also, if carbon has built up in your intake, throttle body, and EGR valve parts, this may cause the problem you are experiencing. Having the throttle body cleaned as and a fuel induction service may help as well. Have a certified technician, such as one from YourMechanic, come and assist you with diagnosis and repair of your car’s rough running at high speeds.

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