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Q: Car is not idling smoothly

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My car is not idling smoothly. While idling, it bounces between 700 and 900 RPM. I have replaced the wires, spark plug, and fuel filter. I think I checked the hoses. I also just changed the upper and lower manifold seals. I have noticed that there are small fluctuations when I am driving on the highway while using cruise control and on flat land. I want to solve this myself and not go to a mechanic. Any ideas?

Hello. This is typically caused by either a dirty throttle body or a bad throttle position sensor. I typically start by cleaning out the throttle body. That will usually take care of the problem. If it persists, I will use a scan tool to monitor the throttle position sensor signal to see if it is failing. That should be the problem. It can also be the air flow meter, but that is not as common. If you want to have someone take a look at it, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your idling issue.

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