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Q: High revving enginge

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So we just got this car out of the garage and it drove perfect all weekend (170 miles). The day after we went to visit family a plastic piece was discovered under the car. When I looked it up on fordparts.com it said it was an air duct. I've looked virtually everywhere I can and can't find where it goes. Shortly after this piece is discovered the engine started revving really high like I was flooring it. We cleaned the throttle cables (that worked for about and hour), we cleaned the throttle body (that's did nothing), we replaced the mass airflow sensor, speed sensor, nothing has changed. The gage on the air cleaner is still green. When we take the air cleaner off it doesn't Rev high.

My car has 150000 miles.
My car has a manual transmission.

A: Hello. Most of the time when this engine st...

Hello. Most of the time when this engine starts revving high all of a sudden, it is because of a vacuum leak. This can occur if any of the vacuum hoses or elbows break. I would need to see a picture of that part to know for sure where it goes. If it is indeed part of the air duct, then it can cause an incorrect reading to the mass air flow sensor which will also cause this.

One other part that will also cause this to occur is a bad throttle position sensor. If this fails and reads incorrectly, then this will occur. I usually check the computer for codes and to check fuel trims to see where the problem is. If you need to have this looked at, consider YourMechanic, as a certified technician can come to your home or office to diagnose the revving issue more thoroughly.

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