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Q: rough idle and low rpms at a stop light, but drives fine

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I have a 2006 jeep grand Cherokee. Drives great but sometimes at a red light the rpms drop to about 750 then lower and shutters then jumps back up. It only does this when im at a red light.

My car has 86000 miles.
My car has an automatic transmission.

A: Hello. This is very common on this particul...

Hello. This is very common on this particular vehicle. Typically it is caused by a dirty or failing throttle body. I have also had a few of these with a sticking thermostat which causes the engine to run cooler than it should and makes the car run like this.

I typically start by cleaning the throttle body first. If that does not take care of it I would use a scan tool to check the coolant temperature and the throttle sensors. If you are thinking of having this done, have a certified mechanic inspect your rough idle and low rpm's to make an accurate fix.

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