My car keeps reving up and down when i am at a stop light or in idle. Does anyone know what this means?
a vacuum leak will cause that. get some carb cleaner, better yet, get some starting fluid and spray around all the vacuum fittings and even the intake gasket, it will let you know when you find the leak, you will feel the difference in the idle.
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If your A/C is running, the compressor could be kicking in and out if your interior air is very near the correct temperature.
That’s the simplest, cheapest explanation. But the other answers before mine are not necessarily wrong. I’m just offering a thought different than what the others offered
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like doc said it could be the a/c if its on. if it only does it with foot on brake it could be vacuum. if it does it in park it could be the Idol speed motor on the throttle body