Engine Vibration

2005 GMC ENVOY
145,000 MILES • 4WD • AUTOMATIC
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NATE POHLEN
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In the past 24 hours, following a long road trip, my car has developed a noticeable shake/vibration (almost like when bass is too loud) only when my foot is holding the break pedal down in drive or reverse gears.

This does not happen while I'm driving, and it does not happen in park. When I am idle at a red light, stop light, or waiting to back up, that is when this noise/feeling happens. I can't diagnose where exactly it's coming from, it feels like it's probably under the hood but I can't look under the hood while replicating the problem with my foot under the break. I have read about motor mounts, engine misfiring, EGR valves, gasket leaks, fuel pump filters, spark plugs. no idea where to begin.
Jun 28, 2019 at 2:09 PM
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STRAILER
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Yep, engine mounts are my opinion here especially with that kind of mileage. Here are diagrams to help you replace the them below.

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Jun 29, 2019 at 7:59 PM
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JACOBANDNICKOLAS
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Welcome to 2CarPros.

Honestly, it is most likely the result of idle speed or worn mounts. Take a look through this link. Also, are you running the AC when you notice it? Here is a link that discusses common causes. See if anything on it helps. Also, let me know if it is related to the AC running, when the last tune up was done, if the check engine light is staying on, and anything you can think of that may help me. Also, some simple things to check for are a dirty or plugged air filter, loose air intake tube, or even a vacuum leak.

https://www.2carpros.com/articles/engine-vibration-at-idle

The next link explains how to replace one. Just make sure yours isn't loose, have any hoses disconnected or leak or anything that can allow unmetered air to enter the engine.

https://www.2carpros.com/articles/how-to-replace-a-car-air-filter

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if you find anything or if you have other questions.

Take care,
Joe



Jun 29, 2019 at 8:10 PM
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NATE POHLEN
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Joe, after testing some of the things you said, here is what I found:

1) This IS only happening when the AC is running. It's 100 degrees every day here where I am, and I turned off the AC and tried to replicate and had no problems. Turned on the AC, and got the vibration again.

2) I opened the hood and had someone replicate the problem while I looked under the hood. Basically it looked like the engine would shake every few seconds. I attached a video (sorry if poor quality), at about 2 seconds you can see the engine kind of shake.

3) I am embarrassed to say I have not had an engine tune-up done yet on this vehicle, and the check engine light has been stuck on for 5 years because I had an issue fixed but they couldn't get the check engine light off and I never figured it out.
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Jul 1, 2019 at 7:40 AM
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STRAILER
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Thanks for the video. it does look like the engine is misfiring causing the problem, also the AC system can be overcharged which will cause this issue as well.

Lets do a tune up first and go from there. here are two guides to help walk you through the repair:

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

and

https://www.2carpros.com/articles/throttle-actuator-service

Please run down these guides and report back.
Jul 1, 2019 at 11:33 AM