Trouble after replacing motor mounts

High engine speed is typical of a vacuum leak, in this case, most likely due to vacuum hose that got bumped and knocked off, or a dry-rotted hose that cracked. The second symptom of late shifting can also be related. With a vacuum leak, vacuum goes down, and that occurs normally during acceleration. Low vacuum equates to hard acceleration, and that tells the transmission to delay all up-shifts to a higher road speed.

There is no diagnostic fault code for a vacuum leak because the Engine Computer is seeing an acceptable, (but wrong) sensor reading. As long as a legitimate value is seen, no fault code is set. The computer can set a fault code related to the results of that leak. The most common code is "running too lean for too long" which is the result of too much air getting into the engine through the vacuum leak. Lean codes take a while to set because they do not want to set nuisance codes every time there is a little glitch in the reading. Regardless if there is fault code or not, we always start by looking for vacuum leaks when you have the symptoms you described.

Thanks for the quick reply. I will bring this up to the mechanic.

Please let us know what you find so it will help others.

Cheers, Ken

So after much time the check engine light finally came on and it was the Throttle Position Sensor. I was told that the car was in something called "limp mode" where the transmission wouldn't let it shift out of first gear but that somehow my engine was still allowed to attempt high speeds.

That should not be related to the engine mounts, but the diagnosis and solution make sense. Happy to hear it's solved.

Good to hear, please use 2CarPros anytime we are here to help.

Cheers, Ken