Car idles rough in gear only when at stop

MARTIN ORTIZ2

MEMBER
2015 HYUNDAI ELANTRA
1.8L
4 CYL
2WD
AUTOMATIC
170,000 MILES

My car Idles rough when I have it in gear, idles even worse when the A/C is on. It would even make the car turn off if I turned the A/C to the highest setting. It no longer turns off just shakes and idles rough. The car also accelerates on its own with the A/C on, like the idle will gradually pick up speed. So far I have changed the MAP, sensor, PCV valve, spark plugs, filter. I have also cleaned the throttle body with the CRC brand cleaner. I wasn't sure on moving the blade manually as it is electronic and I read you shouldn't. My car doesn't seem to open the blade while having the key into the ignition on position while having the accelerator pressed though. I also don't know if I am supposed to do the relearn process. I have tried leaving the battery unplugged over night but I still have the rough idle. I have noticed that the A/C Clutch is stuck engaged all the time and does not disengage. I have tried spinning it by hand as well and it doesn't move. My A/C is still cold. Could this cause the engine to idle rough though and the surge with the ac on? Any suggestions or help would be greatly appreciated.

Monday, August 2nd, 2021 AT 10:26 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

That's a tough one. The idea that the compressor is always engaged regardless if it is on or not can be causing the issue.

Are you certain that the compressor clutch is engaged and it's not just the pulley turning? If you are, disconnect the compressor. See pic 1 below. See if that causes the clutch to disengage and the idle to change to normal.

When the A/C is engaged, the engine idle speed should be slightly increased to compensate for the added load. However, if it is always engaged, that is going to throw things off.

Also, a rough idle can be caused by an engine vacuum leak. Check for that as well. Here is a link that shows how it's done:

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

If none of this helps, then I recommend having the can-bus scanned for diagnostic trouble codes. CAN stands for controller area network. Basically, all the computers/modules are tied together via a few wires. This will retrieve codes regardless of the module it's stored in.

Here is a video showing it being done:

https://youtu.be/InIlnsjOVFA

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

Take care,

Joe

See pic below.

Image (Click to make bigger)