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Engine abruptly revving intermittently (2012, 6 cyl, 3.7L, automatic).

Warranty and Service Issue

Engine abruptly revving intermittently (2012, 6 cyl, 3.7L, automatic).

Old 3/4/19, 04:19 PM
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Engine abruptly revving intermittently (2012, 6 cyl, 3.7L, automatic).

Disclaimer: I'm asking on behalf of my mother, though I've seen this firsthand.

An intermittent issue has been plaguing the car in question for the last six months. Typically goes like this:
  • The rev counter will abruptly begin to climb, topping out at around 3k RPM.
  • The engine will start to sound as if it is accelerating, though the vehicle itself won't change its speed.
  • In conjunction with these two issues, the other gauges will flip back and forth wildly (though this didn't happen with the most recent occurrence).
  • The issue will wind down and cease after a short amount of time.
This tends to happen when the car accelerates from a stop, or while it's already at speed. Additionally, this happened before the cold weather set in, indicating that the problem isn't cold-related. Car's been through the dealer and two local mechanics, the latter of which are very highly-esteemed and generally good at diagnosing problems. Computer isn't throwing any errors, and because it's so intermittent (it's happened maybe 10 times within the last 6 months), it's been impossible to replicate. Terminals are clean, too, though the battery itself hasn't been replaced (to my knowledge).

I suspect that it may be the PCM/ECM, given that whatever's causing the problem appears to be non-mechanical, but I've also read that it might be the FSU. It's the most bizarre issue that I've ever seen and heard of. Seems strange that nobody has caught it up to this point. I'll try to be as helpful as I can.

EDIT: Forgot to add - car's got 80,000-ish miles on it and is a DD, regular maintenance, up to date on all recalls.

Last edited by MattJL; 3/4/19 at 04:24 PM.
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Old Today, 10:26 AM
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This is for a 2011 but may be the same as yours. Check these grounds in the engine compartment. http://iihs.net/fsm/?d=711&f=010%20-%20Grounds.pdf
You may find the locations here; http://iihs.net/fsm/?d=711&f=151%20-...on%20Views.pdf
Sometimes the painted surface under the ground terminal blocks continuity. I would remove the terminal and clean the paint only where the terminal sits and the re-tighten the connection. At the least, loosen and re-tighten the bolts clamping the terminals. This will give a new bite to the body panels and give you a chance to see if it corrects the problem.
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My 5.0 at one time wanted to occasionally rev between 500-1500 RPMs. Cleaning the throttle body fixed the problem. The issue I had isn't exactly what you are describing, but it might be worth investigating.
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