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Q: Misfires at idle

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I have a relatively new truck that's idling rough. If I'm sitting still, it stays at around 500 rpms, but every few seconds the needle dips and goes back up. I've been to the dealership several times, but they keep telling me it's normal. I have another chevy truck that doesn't do this. One line they're feeding me is that the engine deliberately misfires one cylinder while it's idling to do some sort of diagnostic check every few seconds. Is that true? If not, what else can you suggest as a cuprit?

Hello. This engine does do a series of self-tests, but you should not feel them. Since the idle is so low, I typically check the throttle body as it may be defective since the vehicle is still so new. If that is fine then I would typically start by reprogramming the vehicle’s computer. If the problem is very subtle, then it is normal. If it is very well-pronounced, then you need to get GM’s service center involved if the dealer is not helping you with this, as your car should still be under warranty. Alternatively, a technician from YourMechanic can diagnose your engine’s misfire and determine exactly what needs to be repaired for you.

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