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Q: My truck will sometimes run in park but whenever I switch gears. It dies when going into either drive or reverse

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My truck is dying in drive and reverse and sometimes won't start while it's in park.

My car has 143000 miles.
My car has an automatic transmission.

Hi, thanks for writing in. A weak idle is most often caused by vacuum leaks in the intake system. This can be a loose or leaking vacuum hose (including hose to modulator on the transmission), leaking or stuck open exhaust gas recirculation valve, or base gasket for the carburetor. The foundation of course is that the engine is in good tune otherwise - ignition timing is correct, good plugs and wires, carb is in good shape. Spraying starter fluid around suspected vacuum leaks with the engine idling is a quick diagnostic trick - engine will speed up if starter fluid is being pulled into a leaking hose or connection. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

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