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Q: When I start my truck it's idling high and when I'm driving the rpm fluctuate up and down and the transmission doesn't want to

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My truck seems to be idling high when I'm driving the rpm fluctuate up and the transmission doesn't shift right shifts hard then sometimes want down shift I've changed the throttle position switch and the air intake switch nothing still the same could it be a transmission switch

My car has 170000 miles.
My car has an automatic transmission.

A: Hello. It sounds like you may have a vacuum...

Hello. It sounds like you may have a vacuum leak. This engine is notorious for vacuum leaks from a bad intake manifold gasket. This is very common. It can also be from the MAP sensor or a number of other things. I usually test for vacuum leaks first as I have seen this the most. If you want to have this checked out by a professional, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose the high idle and hard shifting so that these issues can be properly addressed.

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