High idle

PRAY4ME

MEMBER
2002 JEEP LIBERTY
3.7L
V6
4WD
AUTOMATIC
195,000 MILES

I have replaced the IAC. Two to be exact, got a cheap one from Rock Auto didn't fix the issue. Decided to try a IAC unit from AutoZone thinking of better quality. Still have an high idle. At idle the rpm's are around 1,500 to 1,700. I have tried to leave the battery terminals unconnected for two days and when reconnected the check engine light will turn on as soon as I start the vehicle. Before If I leave the battery disconnected for that time frame, the computer would reset and the check engine light would not turn on as soon as I started the vehicle. During driving the vehicle on the interstate on level ground the vehicle can almost maintain 60 mph without my foot on the accelerator pedal. The computer has been scanned twice, once at Advance Autoparts and a local Jeep dealership with the code showing IAC. One of the odd symptoms is when I'm driving on the interstate if I accelerate rapidly bringing the rpm's pass 4,000 to 4,200 and let off the throttle the vehicle will go back to idle rpm's for 5 to 7 seconds then return back to 1,500 to 1,700 rpm's. What am I missing?

Tuesday, November 12th, 2019 AT 5:21 AM

3 Replies

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

A high idle or a "searching" idle can be the Idle Air Control[IAC] valve, OR, the wires associated to it. Another thing that causes this condition is an intake or vacuum leak. Here is a link below explaining what a vacuum leak is and how to find and fix it below:

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

If the problem isn't an intake or vacuum leak, and it is still the IAC valve, then the problem is going to be, more than likely, in the wiring going to the IAC valve. In the diagrams down below I have included a wiring diagram of the IAC valve, and guides with how to find opens, short to grounds, shorts to power, intermittent and connector problems, and how to find unwanted resistance in an automotive electrical circuit using the preferred method, voltage drop. You will need to use a Digital Multi-meter to do these tests, so here is a link below explaining how to use one, if needed:

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Please go through these guides and get back to us with what you find out.

Thanks,
Alex
2CarPros

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Tuesday, November 12th, 2019 AT 5:10 PM

PRAY4ME

MEMBER
7 POSTS

Hello Team,

What I found was one terminal inside the connection for the IAC valve was not making full contact with the replacement IAC valve causing the computer to keep giving me the error code for the idle valve issue. The vehicle idles well when first start when cold, after the engine warms up I still have a idle around 1,500 rpm's. Did not find any vacuum leaks, I have a new air filter and throttle body has been cleaned twice.

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Monday, January 27th, 2020 AT 5:12 AM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello again,

That still sounds a little high to me. Usually this indicates a vacuum leak. A good way to find a vacuum leak is to get a propane torch and barely crack it open, making sure not to light it. Pass it by the air intake tract, intake manifold, vacuum hoses, and EVAP hoses. When it passes by the vacuum leak, the engine will rev up as the engine digests the propane. Please get back to us with how everything turns out.

Thanks,
Alex
2CarPros

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Monday, January 27th, 2020 AT 3:10 PM