Waynerd

So 98 xj, 4.0/Aw4. Drove it several times today. About. 2 miles around 11 am, maybe 6 at 2:00 and about 2miles around 6. Then about 10:00 I go to take a drive. It starts and idles as usual. Let it idle about a minute or two. As I'm pulling away it cuts out a bit. Then as I stop at a light it stalls. Restarts hard. Drive about a mile and its hesitating like crazy like fuel is cutting out. Did what I had to do, it barely drove and wouldn't stay idling and I needed some input on the pedal to get it to start and stay.

Get home and pull codes. They are p0123 and p0505. First is for TPS voltage high and second is IAC malfunction. Going out in the cold dark to do some quick inspecting. Only out of ordinary today was that it was sprinkling/ drizzle for most of the day.

A while back I had issues with the TPS and I ended up pulling the horn fuse and it was fine after. Tried swapping the TPS first with no change. I don't have cruise so there shouldn't be anything else supplying voltage to the clockspring I think. ?

Curious to know if these codes often are combined or what condition besides faulty wiring would cause both. Any ideas are much appreciated.
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Waynerd

Checked and wiggled wiring. Saw nothing, changed nothing. Pulled off intake air tube, nothing sucked into throttle body. Also sprayed some throttle body cleaner around in tb and no change.

CCKen

If you want you can perform the TPS tests outlined in the image below.


Use a safety pin to back probe the connector wires.


Review the procedures before beginning.



.

CCKen

This is resistance checks of the IAC stepper motor, performed with the IAC connector removed.


You can also check to see if there is battery voltage at each connector pin cavity with the ignition switch to RUN/ON, engine not running.



.

Waynerd

Thanks for the references ken. Will be heading out to the cold dark driveway to do some testing I guess. Funny though, I stopped home on my lunch break today and it fired up and idled ok. Took it for a drive this evening and it idles now but still a bit of cutting out when accelerating and wants to stall when slowing to a stop. Will fire and idle fine. Only thing that changed today was it sat in the sun all day. Only place it may have gotten wet is where water leaks behind the dash on the drivers side. Not sure if there's anything there that would get funky if it gets wet. Definitely been through some heavy rain storms and this never happened. Will report my findings.

Waynerd

No luck with back probing. I popped the connector off and tested it. Engine off key on:
Cavity 1: 0.15v
2: 4.71v
3: 5.25v
I know cavity 2 is the signal and I understand by back probing I am reading the signal from the TPS. But should the supply to it be so high?

Waynerd

If I have some time tomorrow before dark I'll try and back probe it. Then I'll have a helper too so I can check WOT. Also will put the TPS I removed back in since when I switched them the TPS wasn't actually bad, it was my clockspring. Haven't changed the clockspring yet either. But the reading at the ground was within spec anyway.

Waynerd

So I've noticed something today. When I turn the steering wheel a couple turns the TPS acts up. I already have the fuse and relay pulled for the horn. No cruise control. So what else could be spiking voltage in the clock spring? I know the fix is to install a good clock spring. Don't have time or money for that now though. Just need to keep this thing drivable until I get my other 98 on the road. Gonna try pulling the airbag relay.

CCKen

How do you know the TPS acts up?

CCKen

Did it ever have cruise control?


Check the voltage input to the TPS at the Brown/Yellow tracer wire when turning the steering wheel - key to RUN. There should only be .015 to .020 volts on that ground circuit wire.


The clockspring is tied into the ground circuit, but only though the cruise control circuit.

Waynerd

By TPS acting up I meant it starts to cut out under throttle and wants to stall. I thought I read it could pick up voltage through the horn wiring also. Anyway I pulled the two fuses for the airbag and now it's not having any problems. Didn't think any power was fed to the clockspring through the airbag circuit but pulled the fuses just for ***** and giggles and it either worked or it's highly coincidental. I'll pop those fuses back in and see if problem returns. I'll do some further testing also. But Ken, what about the 4. Something volts I'm getting to the signal wire for the TPS? Tested with the connector removed from TPS. Is that normal? And to answer your second question, I don't think it ever had cruise. Not unless the steering wheel was changed. Highly unlikely but one never knows what could have been done previously.

CCKen

Don't know about that 4.7 volts on the signal wire. Never bothered to test mine. I'm wondering if it isn't a feed back from the TCM somehow.


The wiring diagrams do not show the airbag circuit going through the clockspring but the driver's airbag sure is right there so there could be some monkey motion going on in the steering wheel.

Waynerd

Okay. Jacked the front wheels off the ground. Replaced the 2 airbag fuses. Tested all 3 pin cavities with the key on. Got the same readings no matter how I had the steering wheel. So I plug the TPS in. Started the jeep. As soon as the wheel was turned as far right as possible it sputtered and stalled.

Turned the ignition off, unplugged the TPS. This time the reading at the center cavity is 5.62 volts. Not sure what this means though. Lol. Going to remove the 2 fuses and try it again.

Waynerd

Now it gets interesting. I turn the key on, wheels are still in the same position as when it stalled. Center cavity is still reading 5.62v. Then I turn the key off. Pull the 2 airbag fuses again. Still haven't moved the wheel. Turn key on. Check the center cavity again and it's now reading 4.71v. SMH


It's as though I may be on to something. Just not sure what. Is there a place other than the clockspring where these issues could happen aside from the clockspring?

Waynerd

Pulled the TPS plug from my other 98 last night and center cavity reads 4.70 v. So that's normal it seems. Not sure where the voltage spike is coming from