1990 Jeep Cherokee

I paid $20,000 for this Jeep. It always would, upon startup rev higher than I thought it should. Even had sudden unintended acceleration a time or two. the dealer did not find a problem. I never thought it would make it to 212,000 but here we are. My mechanic told me to never bring the beater back and it was about to die and that’s why it revs too high, but only when it is warmed up. His suggestion was to replace the rear wheel brake cylinders so now I can stop it fine, but I don’t think it should be turning 2,000 rpm (a guess) “at idle” He says there’s no vacuum leak. I asked about a possible intake gasket leak. He says no and again tells me to not bring it back. He says the reason he cannot get the idle down is because the motor is so bad. And yet it gets me back and forth every day faithfully roaring. Do you know that light bulbs burn really bright just before they go out and distant stars do the same? Is it possible that this old Jeep is cosmic-ly so connected that it is fixin’ to go out like a super nova or 60 watt bulb? Thanks, Dave.

I think your mechanic is at a loss. Try another mechanic. You could disconnect the electrical connector to the idle air control valve (iac) and see how the engine runs, then. It wouldn’t, necessary, mean a bad iac valve. The iac valve could be doing just what the engine computer is telling it to do (too-high an idle). I have nothing good to say about the dealer…how many years did it have this problem?

I recall a tsb on that vintage Jeep re throttle position sensor causing hi idle speeds. It’s likely that I have replaced them on several 4.0Ls including some of my own, I have owned several dating back to 1988. All were safe, reliable vehicles and all were driven well over 200,000 miles. Find a mechanic who appreciates “heavy metal.”

Absolutely right. “Never bring the beater back.” ???!!! How can this guy possibly fix your Jeep with this attitude?! Your supernova analogy is really poetic, but sorry, it’s got nothing to do w/behaviour of Jeep. Warmed up, an engine idle of 2000RPM is way high- 800’s more like it.

Consult people you know and get a reccomendation on a good mechanic; or; go to bottom of this page, click on “home”; then on homepage about center right of page click under “Find a reccomended mechanic” and you gotta put in your zip. (“Never bring the beater back”)!!! God, it boggles my mind…

The iac was the first thing he did. He even came to my house to work on the thing. And spent way more houirs on it than he charged. Some stuff he put on at his own expense. Bought a new diagnostic computer. Did a bunch of stuff that I don’t understand. And the computer is telling it to idle high but only when it has warmed up. Mechanic replaced the on board computer at his expense. The high idle is recent. Within the last year or so. The high rev at start up has been since new. I drove this Jeep for Eight years and gave it to my daughter. She parked it after she drove it and it sat for a year or two and she gave it back and I’ve been driving it a year or so as a beater/canoe hauler/fly fishing mobile. I have decided that when the license plate expires in Nov '08 I’ll give it away or junk it out. I think I am inspired to tae it to another reputable mechanic I know of in my area. And if he tells me to not bring it back—well, at least I’ll know. Thanks for the input.

Well, the guy sounds like a good guy after all. But I’d agree you’d be better off w/a new mechanic. Somehow your Jeep seems to have a lot of “Character”. I’d hate to see you junk it. Oh well, good luck!

You paid $20,000 in 1990? Wow, you must have REALLY wanted it!

Be that as it may, if your mechanic tells you “to never bring the beater back,” you need a new mechanic. Simple as that.

At 212K miles, anything is possible. Is this thing fuel injected or carbureted? Either way, you’re right, it should not be idling at 2,000 rpm. Find another mechanic.

What about a hanging throttle cable or cruise control servo cable? You might try forcibly closing the throttle plate by hand while it’s idling at high RPMs and see what happens.
Since a vacuum leak could also cause this the first thing I would do is connect a vacuum gauge and rule that out or in since this is about a 2 minute job.

I would also hope during all of this that the throttle stop screw has not been dinked with since said screw is not supposed to be dinked with at all except under certain specific circumstances.

Since it only happens when the engine is warm, the coolant temperature sensor and its wiring should be checked. Some vehicles have two sensors; you want to check the one for the engine control computer, not the gauge if yours has two.

The TPS also merits a checkup.

There was a SAFETY RECALL #301T in March 1991, on the 4.0L engine for a defective TPS (Throttle Position Sensor) because it, “…may experience an intermittent high idle condition immediately following engine start.” Sound familiar? When the new TPS is installed, it has to be "…adjusted to 12-14%…using the DRB II ". Jeep (and Chrysler) dealers are about the only ones who have the DRB II scan tool to set the TPS with. In a way, your mechanic didn’t have a chance. You should have received a SAFETY RECALL letter in the mail, if your Jeep was one affected by the recall. Even if not covered by that recall (call Jeep dealer to find out), it’s a good chance the TPS in your Jeep matches those symptoms.

Here is a copy of the TSB which was later turned into a recall.

It’s reassuring to know my memory hasn’t failed totally, 'kit.

The warranty administrator at the Chrysler-Jeep dealer I worked at had a saying-“Once a recall always a recall” (Some exceptions); so call Dealer pronto before greasing any more garage’s palms. Good luck to you and the beater.

You guys ROCK. I’ve been taking notes and will follow up. It is injected. The tps has been replaced. BUT not sure if the latest one was set properly. The throttle screw had been dinked with. I drove this car for 8 years, gave it to my daughter and she gave it back to me to use as a beater not quite two years ago. My mechanic asked me "who dinked with the throttle screw? " He re set it. I’m pulling my repair paperwork and going over it closely. They were costing about 20,000-24,000 in 1990. I bought it new. My '94 Grand Cherokee was 27,500, down from 32,000. The 2006 was discounted to about 30,000 with no interest loan.

With this advice I am more empowered to get this thing running right.

You paid $20,000 in 1990? Wow, you must have REALLY wanted it!

I was thinking the same thing…I bought my first Pathfinder in 1990…I looked at the Cherokee back then and from what I rememeber it was cheaper then my pathfinder which cost me about $18k.

WHEN was the tps (throttle position sensor) changed? Years ago? Recently? Today? If it was changed before the current problems, the replaced one could be doing the same as the original (it could be in it’s DNA). The tps can be checked with a digital voltmeter (multimeter). It’s not that difficult.

TPS was replaced recently and years ago. Actual price from my window sticker is Base price $15,545.00 Imagine that. With options it was $21,634.00 My sales statement shows my actual price was $18,550. plus tax, title etc. That was 12/21/1989. I have about 14 warranty repair orders and/or recall repair orders. The regular repair orders show that I had it in the dealer in 1996 for this high idle when warm issue. Also, at around 146,00 the dealer quoted a price of $1200 to $1400 for a new short block because of the piston slap. I still think it was the valve train clatter common to the 4.0 L engine. Well, I never did have the shortblock done and this motor has not had any major repairs. In looking back on all my repair work I have to question my loyalty. Now I know where they get the phrase, “It’s a Jeep thing”. My other two Jeeps have been much more trouble free, especially the '06. But I thought this Jeep was reliable and trouble free.Until I looked back over the paper work. I have been taking notes and am going to have your ideas checked out. I am happy to get all the pointers. Regards to all.