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?
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
DO NOT ADJUST THAT SET SCREW!
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.
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...
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.
95 ZJ 4.0L 3 inch Lift
99 XJ 4.0L 4 inch Lift
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...
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?
1996 ZJ Green Laredo V8, 2.5" OME and Bilsteins, 33's, Holes drilled in the roof.
1998 ZJ Platinum Limited 5.9, Backyard parts fodder
1987 Mercedes 300D Turbo, the diesel daily, 30mpg in style
Originally Posted by Texas ZJ1
I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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!