RPM surging at idle

Tiny
PETER_1776
  • MEMBER
  • 2015 MITSUBISHI OUTLANDER SPORT
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 105,000 MILES
Whenever I am at a stop light or stop sign and I'm sitting at idle, my RPM will drop to below 500 then jump up to 800 or 900. And this will continue over and over until I start moving forward. I've noticed that if I turn of the AC it will help most of the time. And sometimes it helps if I put it in park. And if I have it in park with the AC off, no surging down and up. So does it have something to do with the AC?
Sunday, May 26th, 2019 AT 4:38 PM

2 Replies

Tiny
PETER_1776
  • MEMBER
  • 2 POSTS
The car will jump a tad forward on its own when the rpm goes down and up. And I've noticed it will be more jerky when I accelerate it forward. And, not sure if relevant, I will hear a click when the rpm goes down and up.
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Sunday, May 26th, 2019 AT 5:36 PM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This sounds like you could have a vacuum leak. A good way to test for a vacuum leak is to get a propane torch. Using extreme caution have an assistant start your vehicle as you crack the propane torch open, making sure not to light it, to it's lowest setting. Run the torch along the air intake duct, intake manifold, vacuum lines, and EVAP lines. When the torch passes by the leak the engine rpm's will rise as the propane gets ingested into the combustion process. Repair the leak. I have also included a link below for you to go to:

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

Please go through the guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Sunday, May 26th, 2019 AT 7:00 PM

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