Trouble after replacing motor mounts

CAMJEM

MEMBER
2005 KIA SPECTRA
4 CYL
AUTOMATIC
113,500 MILES

Hi, I recently had my motor mounts replaced and now my car is having problems switching gears it seems and revs up to 3000 or 4000 while driving (40 mph) before dropping back down to about 2000. I was at a red light and the car starting revving going as far as actually moving the car while my foot was on the brake. This was never an issue before the mounts were replaced. I took it back to the mechanic and he hooked it up to a computer and it did not read anything wrong. The check engine light never came on while out driving it either. Also, he checked the transmission for any leaks and there were none. Any suggestions?

6 Replies

CARADIODOC

MECHANIC
33,871 POSTS

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.

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Friday, April 21st, 2017 AT 7:03 PM

CAMJEM

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3 POSTS

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

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Saturday, April 22nd, 2017 AT 8:02 AM

KEN L

MASTER CERTIFIED MECHANIC
47,536 POSTS

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

Cheers, Ken

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Monday, April 24th, 2017 AT 9:39 AM

CAMJEM

MEMBER
3 POSTS

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.

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Wednesday, April 26th, 2017 AT 3:07 PM

CARADIODOC