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