Drivability problem in a 98 XJ. . .

This continues another thread I started, in which I was considering buying a '98 XJ, auto transmission, NP242, located here:

http://www.naxja.org/forum/showthread.php?t=935114

Initially, I thought it had a transmission problem, as when it was cold, it would drive really poorly, bucking when you tried to drive at more than an idle, not shifting properly. . . then the problem would clear up within a mile of driving while giving it short bursts of throttle.

I've had the opportunity to observe its dysfunction a little more now and I've picked up on these tidbits of information:

1) It starts fine. If I don't touch the gas at all from start through warm-up:
2) It idles fine for about a minute.
3) After that, it idles very roughly, seems like it's going to die, and smells especially rich during this rough idling stage.
4) It then surges up to above 1000 RPM, then slowly drops, and from that point forward, can be driven without any problem.

I hadn't tried a complete warm-up before. All I knew was that it drove very poorly, and that the symptoms would suddenly clear up. I've tried this warm-up technique several times with exactly the same results. If I let it smooth out its idle first, it will give me no issues when trying to drive it. Based on this, I'm thinking the idle air control valve. I tried to use Deep Creep (Sea Foam in a spray can) to loosen up crud on the valve, but I just sprayed it into the slit on the throttle body that leads to where the valve sits, with no generally helpful effect. My next move would be to take the valve off for a more thorough cleaning than would be possible using this possibly flawed approach. I'm sure I've seen threads on cleaning it here.

Anyone think I might be headed in the right direction here?

--wavingpine11

I think the right direction to be going in is to find out why there are no trouble codes.

Does the check engine light even come on?

Slo-Sho said:

Does the check engine light even come on?

Click to expand...

I was just asking myself that. I'm pretty sure that it does come on for a moment when I start the vehicle. But I'll double check that at lunchtime and let you know. I'll run the check for codes if it does not.

But would a faulty IAC valve throw a code?

On an OBDII vehicle...if you sneeze or fart the wrong way it will throw a code.

Realistically, if you pick it up I would pull the throttle body, take it in and clean it out, complete tune up of cap, rotor, plugs and wires plus all fluids changed to correct ones. I don't like the sound of the clockspring and airbag thing, I'd get that fixed asap and no bones about it, could be a bomb waiting to go off in your face. Now that air bag light could be the self docking plugs on the back of the panel but usually when that issue crops up the airbag light comes on the gauges go dead and the odometer and speedometer stop too. I would also just replace the sensors on the TB and check the TPS with a meter, it may be OK. The other issue is it got a new/used engine, I wonder if the installer nicked the CPS on the bell housing while either pulling the old one out or putting the new one in. That can create all kinds of havoc.

Just to clarify, I did end up buying this for $2500, so it's 100% my problem now!.

Update: my check engine light works, but was not illuminated. I checked for codes and got 1. P0463 Fuel Level Sensor A high input. Sometimes the fuel gauge shows that the fuel tank is empty when I first turn the truck on, but then it creeps up to the correct level after a few minutes. Not sure if this is a related or unrelated factor, but it's certainly worth mentioning since I'm most likely dealing with a fuel, air, or transmission problem.

Anyone care to comment on my assertion that it is not likely the transmission given all the new information I've picked up?

It sounds like it is probably one of 3 things, In order of likelyhood:

TPS: Won't throw a code always
CTS: Perhaps not reading correctly until warmed up a little bit, IE thinks it is -40 out even though it isn't
CPS: It sucks and I pretty much beleive it can cause any problem on a jeep, including rusting body panels and crappy radio reception.

RichP said:

Realistically, if you pick it up I would pull the throttle body, take it in and clean it out, complete tune up of cap, rotor, plugs and wires plus all fluids changed to correct ones. I don't like the sound of the clockspring and airbag thing, I'd get that fixed asap and no bones about it, could be a bomb waiting to go off in your face. Now that air bag light could be the self docking plugs on the back of the panel but usually when that issue crops up the airbag light comes on the gauges go dead and the odometer and speedometer stop too. I would also just replace the sensors on the TB and check the TPS with a meter, it may be OK. The other issue is it got a new/used engine, I wonder if the installer nicked the CPS on the bell housing while either pulling the old one out or putting the new one in. That can create all kinds of havoc.

Click to expand...

That's sounding pretty sensible about the airbag. I'm waiting on a new steering wheel (the leather on the old one is heavily ripped at the top and overall flaking the top layer off and looking like crap) before I investigate that issue. I don't assume that anything the seller told me was true about the airbag, but I'd be willing to check when I replace the wheel. Are there any wires that one must attach to the actual airbag in the region of the steering wheel?

Besides the TPS and IAC, what other sensor is on the TB?

Also try letting the fuel pump prime, then starting, see if that helps. I would also get a fuel pressure tester and test it during cold startup, could be just a fuel pump crapping out, but overall it seems like the transmission is not getting the correct signals to know when / how hard to shift.

Wildmatt said:

It sounds like it is probably one of 3 things, In order of likelyhood:

TPS: Won't throw a code always
CTS: Perhaps not reading correctly until warmed up a little bit, IE thinks it is -40 out even though it isn't
CPS: It sucks and I pretty much beleive it can cause any problem on a jeep, including rusting body panels and crappy radio reception.

Click to expand...

So with the TPS do I just look for a smooth resistance curve?

CTS? What's that? C_______ Temp Sensor?

CPS. . . had to replace that in the 92. In that case, it was burnt through insulation, and the symptoms were (prior to no-start) that the engine would die instantly every time I splashed through water (intermittent short from the water). So I guess the sensor itself was fine in my case, but not the wires. But why would it only happen when the engine was warming up? Seems like the relationship between the CPS and the flywheel isn't changing any during that time.

Sounds almost exactly like what happened with my 98.

http://naxja.org/forum/showthread.php?t=99655

Start it up, runs fine for a minute. Then the idle starts jumping all around, almost stalls etc. Short bursts of throttle ok. Then it gives a little rev up, and it's fine.

Turns out it was something screwy with the heater circuit in the upstream O2 sensor causing strange feedback. Check out post #15...

Gas gauges in 97's and 98's were poorly done, in the case of 97 they had a recall on them, mine was built in sep 97 so I know it got 97 parts but no recall.
The resistor material on the sender goes bad, results in incorrect readings.
On the Throttle position sensor look for any dead spots or increases or decreases throughout the travel, it's just a variable resistor in there.
Pull the tb, take it inside, remove all the sensors, clean the TB with a good cleaner, if cleaning the other sensors make sure you use cleaner that plastic safe, most of those cleaners eat plastic.
For the 02's just replace them with Bosch which I understand it what the factory uses. Then I would do the tune up. Make sure to use the Champion plugs, some of the other brands and platinums can cause weird issues. These jeep engines seem to run best on copper core champions. Make sure the distrubutor cap has the brass contacts and not the aluminum ones, again dealer or NAPA. You have to get it back to it's 'baseline' or as close to OEM as you can, it could be a combination of aftermarket plugs, wires, cap, rotor, etc that together can cause problems.

98XJSport said:

Sounds almost exactly like what happened with my 98.

http://naxja.org/forum/showthread.php?t=99655

Start it up, runs fine for a minute. Then the idle starts jumping all around, almost stalls etc. Short bursts of throttle ok. Then it gives a little rev up, and it's fine.

Turns out it was something screwy with the heater circuit in the upstream O2 sensor causing strange feedback. Check out post #15...

Click to expand...

Hmm. Hadn't considered that. I checked out your post and it seems like our symptoms line up pretty well. Since I don't know the Jeep' s history, an O2 sensor seems like a good idea anyway on a 155,000 mile vehicle.

wavingpine11 said:

Hmm. Hadn't considered that. I checked out your post and it seems like our symptoms line up pretty well. Since I don't know the Jeep' s history, an O2 sensor seems like a good idea anyway on a 155,000 mile vehicle.

Click to expand...

Odd, I think I was nearing 160,000 at the time...

Good Luck :cheers:

RichP--I'll keep that in mind. My plan thus far is to replace the TB and O2 sensors and the IAC valve and then do the tune-up, but this will probably be after I get paid at the end of the month. Until then, I won't know much more than I do now. On the 98, do I need a special O2 sensor tool or will a wrench work as in the older XJ's? I know on my Subaru the sensor requires the special socket with the cutout for the wire since there's a heat shield blocking access to it.

The sensor is easy, a socket with a cutout makes it easier due to the wire. But if you are definately replacing it, you can cut the wire at the sensor as it will be replaced with the new sensor's wires. Then, you can use a standard socket.

I just got a 98 as well.

It drove ok... but the airbag light was on all the time too. Turns out, there was a recall for 97 and 98s (maybe 99s... I dunno). They move the airbag control module from under the drivers seat to under the console and replace it too. That's what was causing my airbag light. Check here first:
http://www.jeep.com/webselfservice/...recall&country=us&emailUrl=goToEmailForm('R')

Plug in the last 8 digits of your VIN and see what it says. I got the airbag module replaced and relocated, and brand new front brake rotors (different recall). Check that for the airbag thing.

On the driveability thing, I had a 98 TJ, which my mom now drives, and she has the same exact dang problem. The upstream O2 sensor has been replaced in her case... because the wires had melted against the header. And no change at all. At this point they have even replaced the computer and it still does it to her. I'm wondering if the XJ and TJ could have the same issues....

over2land said:

I just got a 98 as well.

It drove ok... but the airbag light was on all the time too. Turns out, there was a recall for 97 and 98s (maybe 99s... I dunno). They move the airbag control module from under the drivers seat to under the console and replace it too. That's what was causing my airbag light. Check here first:
http://www.jeep.com/webselfservice/jeep/index.jsp?screenName=recall&country=us&emailUrl=goToEmailForm('R')

Plug in the last 8 digits of your VIN and see what it says. I got the airbag module replaced and relocated, and brand new front brake rotors (different recall). Check that for the airbag thing.

Click to expand...

Thanks for bringing that to my attention. When I get home tonight I'll check that out.

over2land said:

On the driveability thing, I had a 98 TJ, which my mom now drives, and she has the same exact dang problem. The upstream O2 sensor has been replaced in her case... because the wires had melted against the header. And no change at all. At this point they have even replaced the computer and it still does it to her. I'm wondering if the XJ and TJ could have the same issues....

Click to expand...

It's definitely frustrating. I bought an O2 sensor this morning along with (Champion copper) plugs and wires and I'll be checking the distributor cap as well. I don't think it's a cap issue since it's related to the vehicle having been warmed up or not, but I'm going to check.There are several other things that have been suggested here, so at least I'm not at the end of my options. I'll be much more sad then.

I changed the plugs, wires, and the O2 sensor today, and then got my back-up lights to work again by following the cleaning instructions I found here on . At first I screwed up the installation of the spring loaded terminals on the wiper arm, and the Jeep would start in every gear as well as in park and neutral. . . the copper terminals had slipped out of their slots when I reassembled it and they were just kind of floating around in the dielectric grease. Proper attention to detail, and the back-up lights now work for the first time since I've owned it! I also checked the TPS indirectly by using the view data function on my OBDII scanner. I moved the pedal through its entire range as slowly as possible, looking for any glaring discontinuities in the values, both sweeping up and down. I'd say that it was a less rigorous test than testing the actual sensor, but I think it told me what I needed to know.

What I haven't done is actually remove the IAC valve to try to clean it. I couldn't fit my torx screwdriver in the space under the valve. I couldn't get at it with a 1/4 drive torx type bit either. What tool have you guys used to get this off, or is it that I need to take the whole throttle body off to access it?

It needs gas badly and I will attempt to drive it without warming it up to see if anything I replaced today has affected the drivability issue I've been having when I fail to let it fully warm up before driving. To recap in one long run-on sentence, symptoms are noted during the warm up cycle: First, it starts fine, then idles fine, then after a few minutes will idle poorly and slow, as if about to stall, with lots of fuel smell, followed by a sudden high idle that wafts gently down to a regular idle at which time the vehicle can be driven without the hesitation, bucking, and discomfort that is otherwise experienced if one attempts to drive it prior to this cycle having been completed.