Grand Am rough idle

Grand Prix and Grand Am, Bonneville, Montana and Transport.
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Grand Am rough idle

Unread post by Guest » Wed Sep 16, 2020 11:46 am

When I start it up there is a quite slow knocking sound during idle (not very loud). When I shift into drive it knocks and shifts hard into drive. When the car has warmed up and when I am coasting at an average of 40 MPH the RPMs will jump down by about 200 (a small amount) and immediately jump back up. I feel a small and faint jolt in the car when this happens. Any ideas?

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Re: Grand Am rough idle

Unread post by carriedi » Sat Sep 19, 2020 4:43 am

you really need to drive with a scanner on the vehicle. You need to see if the trans is slipping or shifting gears. If you are moving and s steady speed but your rpm changes then the engine reved up without changing speed. That's something inn the drive chain changing.

Knocking sound, well, that's something that someone needs to hear. I would suggest taking it to a local shop and ask if they can come out and listen to the noise. So many things is could be without knowing what it sounds like or where it might be coming from.

the knocking and the hard shifts may or may not be related. What about the title of this post? Does it have a rough Idle too? Is the check engine light on?

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