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Q: RPM drops while driving

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I recently did some work on my truck, new fuel filter, oil, oil filter, valve cover gaskets, spark plug tube gaskets, intake mainfold gaskets, MAF sensor cleaned, throttle body cleaned, and cleaned some dust and dirt off the air filter. About a week ago it started to drop rpm while I drive once i get to speed and the rpms come to the normal 1500-1600. They drop down to 1000-1100 and i can feel it aswell as watch the rpm gauge drop. I am getting no DTC codes or check engine light. I am stuck and have no idea what to check next. Maybe PCV valve? Thanks for any help!

My car has 170000 miles.
My car has an automatic transmission.

Hello, from what you describe it appears that your vehicle may be experiencing some sort of engine performance issue, perhaps a misfire. Usually misfires will cause a drop in rpm, as well as shaking or engine vibrations. This can be caused by many things. If you recently worked on the vehicle, I would go back and double check that all sensors and connectors are properly secured and in good condition. Specifically any that you may have worked on. The next thing I would do is check for vacuum leaks, perhaps through damaged hoses or faulty gaskets. The PCV valve may also cause similar symptoms, if it gets stuck in the open position. If it remains stuck open the engine will have a vacuum leak, which can cause misfires. I would start by double checking all the components you worked on, and then going from there.

If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

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