1988 Jeep Cherokee High Idle

GTHOPKINSON

MEMBER
1988 JEEP CHEROKEE
6 CYL
4WD
AUTOMATIC
18,500 MILES

My 88 Cherokee has hod the following issue of and on for the last year.

Randomly, when I start the car it will kick up to a very high rpm (guessing @ 3k) and stay there like I have the throttle pegged. It stops by one of two ways; randomly as I drive it a bit, or
if I disconnect the wire harness from the stepper motor on the side of the throttle body (see picture) then reconnect it it immediatly goes down.

My first guess was that the stepper motor was sticking, so I replaced it with 2 I got off Jeeps from a local auto wrecker place, but got the same results off both.

It did seem to subside after last summer once I stopped using the AC for some reason, but has returned again. I dont know if it matters, but I have a leak in my AC system that I have not remedied as of yet.

It seems to me that something is telling the stepper to kick the throttle to almost max rpm and by disconnect/reconnect the wires to it I am reseting the stepper. However, I do not know what to check from here to find out what is causing an "open throttle" signal to be sent to that motor!

I dont graduate from college for 1yr and have to drive this till then, so any help would be godsend!

Thank you

5 Replies

BMRFIXIT

MECHANIC
19,053 POSTS

Check the links you may need to try to spray it with WD 40
its under the throttle

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Friday, March 21st, 2008 AT 9:24 PM

GTHOPKINSON

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13 POSTS

Are these links that you have to remove the throttle to get to or are you speaking of the link behind the TPS or the wire harness connections that link to the stepper? Could you be more specific on what/where your referring to please?

Btw thank you for the response =)

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Wednesday, March 26th, 2008 AT 7:54 PM

GTHOPKINSON

MEMBER
13 POSTS

OK, so its a year later and this is still happening with my jeep, but a bit of clarification.

This problem went away during the cooler months, IE from September till March. It just recently started doing this again, now that the weather is getting into the 60's.

The issue is definitely electrical in nature. For some reason the Stepper Motor is being signaled to keep the throttle high. I know this is true because removing the wire connection to the stepper and then reconnecting it causes it to "reset" and come back down to normal idle speed 100% of the time.

Does anyone know specifically what electrical/mechanical section of the engine sends the stepper motor an electrical signal to kick up/down? I cannot back trace the wires to their source.

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Wednesday, April 1st, 2009 AT 1:07 PM

LUMPYIDLE

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4 POSTS

You may need to adjust the throttle position sensor or replace it, Also if you do this be ready to turn off the key when you start it. I have seen one rev very high when it is not adjusted right. You don't want it to scatter/blow.

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Thursday, April 2nd, 2009 AT 11:19 PM

GTHOPKINSON

MEMBER
13 POSTS

Thanks for the suggestion lumpyidle. I have actually checked the TPS for adjustment, and will be looking at it again. I see that the TPS feeds into the stepper motor, but would it be able to tell the stepper to stay pegged at high RPM? As I understand it the TPS regulates when the transmission shifts doesnt it?