Unlikely

Executive Summary:
Barely running 1989 XJ: It ran decent (NO high idle) two days ago before parking. Very high idle after sitting for 2 days. Idles around 3K or so, and wouldn't come down after a few minutes of sitting in place after starting, and a few hundred yards of driving... NOT the case a couple days ago, so something changed and I'm missing it.

DETAILS
After sitting for 2 days, 1989 Jeep XJ wouldn't start. Ran out most of the battery trying to get it to turn over.

Jumped the battery, opened air snorkel after air filter, used a quick squirt of starter fluid, and it fired right up. BUT it idled at around 3,000 RPM and wouldn't settle down. Again: I had run it for about 3 to 4 miles a couple days ago, maybe 15 minutes. (Lots of testing brakes, slow driving, turning, etc. Very little traffic on my route...)

When I shut it down, overall it seems "normal" and was running at under a thousand RPM when idling. (I didn't note the exact number, as it felt within the "normal" range...)

Any idea why a Jeep would run "normal" one day, then a couple days later, start up, and stay at 3K for an extended period? (I did put it in gear after letting it warm up for 3 min or so, and drove it for a few hundred yards before returning home, parking and turning it off... ) I'd guess some type of vacuum leak, but not sure why it worked last time, and is so different a couple days later. (And a wild guess, based on very little direct experience, so open to all "that's not even close" type comments!)

*******
Bigger back story:
I'm just rehabbing a 1989 Jeep Cherokee Limited 4x4 (4.0 L engine). I'm at the start of this journey and ignorant of so much.

Jeep sat for over 2 years, previous owner reported intermittent issues that he never could solve, probably wasn't maintained very well by previous owner and vehicle was basically abandoned at my house. (He did just give me the pink slip...) I think he had no confidence in his ability to find the issues.

I was able to get it started, (replaced spark plugs, verified fluid levels, fogging oil, starter spray, new gas in tank, new master cylinder, brake bleeding, etc.) and drove it a few miles of very light, neighborhood driving, getting a feel for what's working, what isn't.

Overall not bad... Still tons of details, but progress.

I wasn't thrilled with overall temps on my test drive. Watched plenty of YouTube videos on this model overheating and/or needing replacement thermostats. I've purchased a new thermostat, was planning to flush all coolant and replace thermostat today. Needed to move the car when the idle issue occurred, decided to wait to figure out why it worked decent a couple days ago, then after sitting it's now idling so far out of normal range first.

All references, ideas, and/or troubleshooting starting points appreciated!

PS: I can't believe how this community puts out so much great info. Amazing community.

Unlikely

Hey, after writing the message above: I'm wondering if maybe after using the starter fluid, if I didn't get the snorkel reattached properly?

Or maybe I accidentally disconnected some plug on the snorkel that feeds the throttle body (right after the air filter... I may have the terms wrong!)

I'll retry tomorrow, and all ideas welcomed. Feeling silly for not even trying that before complaining here. (Others can learn from my mistakes...)

I should have tried taking that off, putting it back on before writing this, but the light bulb went off right after I pressed "Post".

Oswalla

Pull off the IAC and if it is black and the passage ways in the throttle body just get a new TB gasket and take it off and clean it up good and reassemble. You can take some rubbing alcohol to the pintle of the IAC to clean it also but be gentle and don't twist or pull on it very hard, let the alcohol soak and do its magic.. I assumed you checked the vacuum lines to see if something got knocked loose. Another common vac leak on these 4.0 is the intake/exhaust bolts are loose, put a wrench on them you will tell if they are loose, top and bottom bolts. I have had exactly what you describe and both are regular maintenance items for me now.

You have what is called a Renix era xj, and most would say Cruiser's Tips are the bible of renix xj's. Have a look see. http://cruiser54.com/

downs

Either the IAC is jammed wide open or you have a massive vacuum leak somewhere.

cruiser54

CRUISER'S MOSTLY RENIX TIPS

THROTTLE BODY AND IAC CLEANING

OCTOBER 30, 2015 SALAD 19 COMMENTS EDIT
Originally by TJWalker of CherokeeForum & JeepForum



The Idle Air Control (IAC) is mounted on the back of the throttle body (front for ’87-’90).

The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is retracted, the air control passage flows more air which raises the idle speed. When the valve plunger is extended, the air control passage flows less air which lowers the idle speed.

Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea. This should be part of a normal tune-up procedure and whenever idle/stalling issues are present.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

1. Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a Torx driver (2 bolts; one can be kind of hard to get to). On ’91 and later, it may be easier to just remove the whole throttle body. Be sure to use a new throttle body to manifold gasket when reinstalling.
2. “Gently” wiggle out the IAC from the throttle body. Gasket/O-ring on the IAC can be re-used if it is not damaged
3. Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and oxygen sensors. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.
4. Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner.
5. It is also a good idea to clean the entire throttle body bore itself, the butterfly valve inside of the throttle body and it’s edges, and all associated linkage as long as you have things disassembled.

Revised 1-31-2016

Idunno

The idle air control for the 89 is about $50.00 plus tax. I tried to clean mine but the deposits on the pintle tip, nor on the housing where it seats, were the problem.

Based on the sudden (overnight) change from normal operating parameters to one of a extremely lean mixture problem, I'd say your stepper motor function inside the IAC has failed. I seriously doubt a chunk of dirt fell into the path of the pintle preventing it from extending out to where it needs to be as commanded by the the system. Mine failed in the full closed position and cleaning did nothing. If a person knows their vehicle well and can hear (sense) and slight (insidious) change in idle conditions, then perhaps dirt might be the problem that a simple cleaning corrects. Yours just went to an extreme condition and that isn't dirt, normally. That's a failure of the IAC.

cruiser54

Cleaning the IAC and throttle body are considered maintenance.

I wouldn't replace the IAC just yet.

A bad TPS, or an issue with it's ground circuit can cause the same symptoms. Here's a simple test for the ground circuit which also affects other sensors.CRUISER'S MOSTLY RENIX TIPS

RENIX SENSOR GROUND TEST

OCTOBER 30, 2015 SALAD 12 COMMENTS EDIT

The sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the ignition is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud.

Refreshing of the dipstick tube connection is covered in Renix Ground Refreshing, and the sensor ground upgrade is covered in Tip #6 – Sensor Ground Upgrade.

On 87 and 88 models, you could have a poor connection at the C101 connector as well. See Tip #2 – C101 Refreshing and Tip #27 – C101 Elimination.

Revised 1-31-2016

Unlikely

You guys are AMAZING!

This is a project car for me, and I can't work on it everyday. I'll be testing the ground, cleaning and tweaking, per the notes above, then replace the unit IF none of that works. I love all the references and photos. (THANK YOU!!)

I'll report back with the results ASAP, within a day or three, sooner if possible.

I'm fortunate my property has an extra garage, but it's been used as storage space for a decade, and now being set up to be a real garage again.
Then I'll be able to work from 5 min to 50 hours over weeks, without any issues.
Right now the Jeep is outside, and I can pull it into my daily garage, but that displaces another daily vehicle... Doable but a bit of effort moving cars around. (NOT complaining!)

More news after I do some homework!

Unlikely

I'm working through the steps from Cruizer54 on "RENIX GROUND REFRESHING" and figured out the ground wire from the battery neg terminal goes directly to the dipstick stud on my 89 Renix vehicle.

The other ground wires are there too on the same stud. In the Refresh article (linked above), it implies the battery ground is going to a secondary stud on the engine a few inches away. (I see that one.)

That implies a prior owner moved that wire so all grounding is on the one stud.

I'm thinking it won't matter, BUT I'd rather hear from those with experience. I'm installing additional ground wires today too (per the article)... so I can easily move the wire from the battery back to the other stud IF there is any advantage to do so.

All together? Or battery to one, others on nearby stud?

All input welcomed!

cruiser54

All together is fine.

Remember:
All connections clean and shiny, like a baby's hiney.

Unlikely

Excellent! Grounding Refresh happening today, then on to the next steps. Purchased my "Ox-Gard" last night.

cruiser54

Keep us in the loop please.

Unlikely

Exec Summary:
Almost done with ground refresh, but trouble getting the bolt at the back of the valve cover, to clean up that end of the braided wire. Not sure of the right tool to make that happen.

Details:
Dipstick tube bolt removed/cleaned all wire lugs (only 2 on this one), reassembled with Ox-gard.

Added two new 4 gauge grounding wires:
One from firewall to the a new bolt on the engine block, other from battery to front cross member.
At the firewall, I removed, cleaned up and Ox-garded the bolt and braided wire there.

Issue I'm working on now: Getting to the other end of the braided ground strap (back of the valve cover).

My short sockets won't allow me to get down to the nut (bolt is too high), and my deep sockets are too tall and don't allow me to clear the little shelfy thing on the firewall.

I'm looking at Harbor Freight, Home Depot and Lowes to see if someone sells a mid-depth socket to get back there.

It is tight enough I don't think any box end wrenches or open end wrenches will work, but maybe I'm missing something.

What tools are you using to remove that bolt in the back?

I did add a 4 gauge from firewall to engine block, so maybe I don't need to worry about refreshing that end of the braided strap? It bothers me I can't do it with my current tools (rather than choosing not to do it).

I'd prefer to finish the job, just to know it's all right. Tool/technique recommendations welcomed!

downs

Because of the problem you're running into I ran a new ground from that point on the firewall to the head. The braided one is still there but I have my own as well.

Unlikely

I do see these "pass through" socket sets. Maybe that's the ticket?
https://www.lowes.com/pd/Kobalt-XTRE...cket/999956372

Now I see these are also available at other stores too, I just wasn't searching for the right thing. This makes more sense to me than "mid height" sockets.

That said, if there are better tools, please advise.