Kris_R

Hello everyone. This weekend my XJ's throttle started responding strangely. When I started it, it idled pretty rough for a moment. When accelerating, it surged at 2k, and felt like it had a couple of misfires when accelerating to highway speeds. I had been driving around all morning with no issues, and they all of a sudden appeared after starting when I left the store.

The next morning, from a cold start, it idled pretty rough. I feathered the gas pulling out of the drive way, but when I pulled off the accelerator, she stalled. It also starting hanging up and not shifting into third gear unless I took my foot off the gas completely. So to recap, the symptoms are:

-Rough idle at cold start
-Hesitant throttle at first
-Surging at 2k
-Trouble returning to proper idle
-Trouble shifting

Sounds like the TPS, right? Well I changed the TPS last night, and it did not solve a single issue. I never had the parts store hook up the computer, as my check engine light is always on anyway (bad O2 sensor.) Anyone else have an idea of what else besides the TPS could cause all of these problems?

Red2000XJ

Fuel pressure maybe

Crazy 8s

The TPS needs to be adjusted.

Kris_R

I have a 2000, and it's my understanding that the TPS on 91 and later aren't adjustable?

CCKen

A bad upstream O2S will cause similar problems. Maybe you should address the O2S issue then see if the problem persists.

tjwalker

Agreed. It's best to chase and resolve every code. Failure to do so may leave you chasing your tail when yet another problem/code comes along.

It's confusing enough to chase one code/problem, but put another in the mix and it gets even tougher to sort it out.

jld66

try unplugging the upper o2 sensor and see if that works. if not, unplug the one on the cat (it will run without them) if it is fine, need o2 sensors. thats how i figured out what was wrong with mine after changing my tps. spent 60 bucks on, tps. it was not the problem. dont just leave them unplugged either. get them replaced. you know, emissions laws.

DFlintstone

Not after 90, ususally. I only say "usually" since I've seen a hacked hy-bred on a 90. Anyone can file/slot their tps for more rotation..

Kris_R

I'll check check the O2 sensors, thanks for the suggestions!

The thing that confuses me is these symptoms all came on at once, after the jeep had been running for an hour. Nothing was gradual.

CCKen

You may want to address ground point G101 on your engine. As you can see in the pic below there are several circuits that can cause problems similar to what you are seeing if the grounds are loose or corroded.


Disassemble the grounds and clean the ring terminals with 400 grit sandpaper and reassemble securely.


G101:





While you're at it, you may want to do the same thing for ground G100.


G100:





See if you can get the CEL codes read and post the numbers here.

Kris_R

I had O'Reiley's scan it. It came back with (I don't have the numbers) TPS, O2 upstream, O2 downstream, and catalytic converter.

I've replaced the TPS and both O2 sensors, but no luck. I've also cleaned the ground points as you pointed out, CCKen. As far as the catalytic converter... it doesn't have one. When I bought it, I didn't realize it had a straight pipe welded in. It's been that way the entire time I've had it with no problems.

I'm entirely stumped. I need to get this figured out so I can sell it, as I don't want to sell a vehicle that has problems.

DFlintstone

The surging and, (well any) idle trouble could be the IAC or it's wires/CONNECTOR. Cleaning both the IAC and it's connector is a thought.
Note, I did read in an FSM that powering up an IAC that is not installed, can ruin it.

Crusier57's "mostly renix" tips cover how to do that.....there's a link to that in my sig.

DFlintstone

Well it seems maybe cruiser didn't cover that. This I might have gotten from TJWaker? (not sure there)>>

IAC CLEANING 88
The Idle Air Control (IAC) is mounted on the back of the throttle body. 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 moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, 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.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

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)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

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 is best for this task. 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.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality.

Kris_R

Does this apply to non-Renix as well?

DFlintstone

As far as I know an IAC is an IAC, 87-01..... It might have moved on the TB, I think even my carbed 84 has something like it.