Question about 1993 Jeep Grand Cherokee

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While in park the rpm jumped from 1000 down to around 700 and back up to 1000 what is the issue?

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  • captncavmn Feb 04, 2010

    this issue is also when driving say you are on the road at 40 mph ..your rpms are at say 2000 while driving it will slightly jump from say 2000 rpms to 2200 rpms and back and forth..

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Hi there,

Well the sources of the problem vary, but they are all related to the air intake system and simple to fix. 
1. The idle air control value (IACV) is stuck open or closed. Clean it (inside and out) with brake cleaner. If it still has a problem, replace it or bypass the water hose it uses to warm up the throttle body. This is an easy job to do on the street, but give yourself about 2 hours for any work you do on it AND have access to your ratchet set, screwdrivers, and possibly have a few new/small hose clamps on stand-by, in case one is busted or badly deteriorated. 
An IACV bypass should only be done if you live in a warm climate. Essentially, you re-route the water hose that comes from the motor and to the IACV. The re-route is routing the water from the motor back into the motor. Then you re-route the hose output/input on the IACV back to itself. Again, only do this in a warm climate. 
If you do this and the problem is still there, the ECU has discovered that the tempurature outside is too cold and you need to replace the valve.
2. The air/water return hose on the idle air control valve is busted open. simple... replace the hose/hose clamp. Then bubble/bleed your radiator.
3. The gasket between the air idle control valve and the throttle body is worn out. Replace the gasket if you can get it as a stand alone item.
4. The throttle body valve is extremely gunked up. This is usually an indication that the throttle body valve is sticking, but likely telling you that the IACV is stuck. The IACV sticks for two reasons... Carbon build-up and rust from radiator water corroding the valve. Please post comments if you need more help or information........

Good Luck!!

Thanks

Posted on Feb 04, 2010

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