# AC On Causes Engine to Rev



## RogV (6 mo ago)

I have a 2009 Nissan Sentra with 85k miles. Great little vehicle but my wife & I acquired 2 newer cars, so the Sentra has just been parked for about a year in our garage. Before parking it, I never had any problems with it. I just bought a new battery & tires for it, replaced my brake pads/fluid, topped off my coolant… the basics. Starts right up & seems to run great again. However, the moment I turn on the AC, my engine revs and stays that way until I turn off the AC. This wasn’t happening before, but then again, it’s been sitting for a year.

Anyone have thoughts or experience with this? I’m trying to get it on the road by next weekend. I’m gifting it to someone in need, so trying to save money by doing things myself.

Would this spit out a diagnostic code? Was thinking of cleaning out the IAC this weekend with hopes that it’s just a dirty valve intake.

Any help is appreciated, thanks in advance.


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## rogoman (Dec 16, 2004)

Maybe it needs an IAVL (IDLE AIR VOLUME LEARNING) procedure performed.


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## VStar650CL (Nov 12, 2020)

Rogo is right, but if it's been sitting for that long you should probably clean the MAF and Throttle Body before doing the IAVL. The purpose of IAVL is to calibrate the MAF readings to the throttle plate opening, so a sticky or carboned throttle plate will pretty much mis-calibrate the system and might make things worse instead of better. Don't manually work the throttle plate to clean it, have an assistant work the gas pedal with key-on-engine-off so the motor opens the plate for you. Pay most attention to the bottom edge and back-bottom half of the plate, that's where carbon buildup will be most pronounced. I use a toothbrush.


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