High Idle on Grand Cherokee - JeepForum.com

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post #1 of 11 Old 03-23-2012, 10:48 PM Thread Starter
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High Idle on Grand Cherokee

So I have a 1997 Grand Cherokee with the 4.0 I6. Its my first jeep ever so i'm pretty excited about it. So I'm having issues with a very high idle when i put it in park. Driving is fine except when i put it in park its shoots up to around 2000 rpm and fluctuates around that range. So myself and a buddy of mine who is an ase master tech looked all over for a vacuum leak only not to find one. So then we checked the idle air motor and found it to be pretty stiff meaning it did not move back and forth easily. So we replaced that but its still having the same problem. Could it possibly be a bad tps sensor?

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post #2 of 11 Old 03-23-2012, 11:31 PM
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Those are the three items that cause it.one note, if you try to move the iac plunger yourself you've ruined it. Never move the plunger.

Check the throttle plate to make sure it's fully closing and clean the throttle body as well.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #3 of 11 Old 03-28-2012, 11:22 PM
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I replaced my IAC from Advanced Auto. About $70. New throttle body gasket @ about $3. At the front left corner of the throttle body is a set screw for the idle control. It doesn't need much to set it to a comfortable idle. I had to remove my TBI a couple of times and make minor increment adjustments 2 or 3 times to get it where it idled where I was comfortable with it. I idle at about 700 to 800 rpm's. Mark
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post #4 of 11 Old 03-29-2012, 04:11 AM
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It is NOT an idle adjust. It sets the throttle plate stop at the factory to account for machining variances. The idle is 100% computer controlled, you can not adjust it. Or rather you're not supposed to, you should fix the problem instead.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

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post #5 of 11 Old 03-29-2012, 05:29 AM
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It could be the TPS. Todd4198 had a bad TPS, bought a new one, and replaced it. Upon replacing it, his idle would jump to 2000 RPM in park. It sounded pretty bad changing from park to reverse or drive. He exchanged the TPS for another TPS and the issue was resolved. Apparently, he replaced his bad TPS (rough idle and crappy shifting) for a defective one (high RPMs in park). I want to say it's roughly $30 for the part. Make sure you pull the throttle body to change it. If not, you'll risk stripping the Torx that holds it into the throttle body. Ask me how I know...

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post #6 of 11 Old 03-29-2012, 07:17 AM
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When I changed my IAC with one from discount auto, on start up, the idle went to around 3000, then slowly, a couple of minutes, it settled down to normal. It has to recalibrate itself or something.
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post #7 of 11 Old 09-05-2012, 07:55 PM
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Excuse my noviceness but what is the TPS? My Jeep is doing this as well... it sits around 2.5K or so RPMs.

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post #8 of 11 Old 09-05-2012, 08:08 PM
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TPS Throttle Position Sensor. It is on the throttle body on the end of the throttle shaft. It can be tested by connecting an ohm meter and moving where the throttle shaft inserts. The ohm meter should change smoothly. If it jumps up and down there is a dead spot and it needs replacing.

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post #9 of 11 Old 11-22-2015, 05:26 PM
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Just came across this old posting and found I have the same problem with the TPS (New TPS still has my car with a high idle and jumps up and down while in park.) You said to make sure and PULL the throttle body when you exchange the old with the new?? Please explain...
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post #10 of 11 Old 11-23-2015, 08:39 AM
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He was just saying to install the new sensor in the throttle body with it off the jeep, which would be easier. If you've already installed it then the new sensor is either bad or the TPS wasn't your problem. Did you disconnect the battery when replacing it to reset the PCM? Did you use a mopar sensor?

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post #11 of 11 Old 11-24-2015, 01:55 PM
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High Idle

Thank you for getting back to me. Bought that new sensor online. It turned out to be bad. Went to the part store and purchased an OEM TPS with a lifetime warranty. disconnected the negative terminal and installed it no problem. Happy to report it is now running perfectly. Took the jeep out for a ride to run of some miles and let the PCM adjust to the new sensor and all is well. I appreciate your help!
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