hesitation driving me NUTS!

[mjma]

does it idle ok, or idle high? If the IAS/AICV is bad, it can get goofy like that. Mine was idling real high after startup, and would have bad hesitation if I gave it light throttle. full throttle was ok, but light/medium throttle would be rough until it warmed up.

TPS is usually more of switching between gears for no reason, or locking you out of OD or 3rd. (sudden drop to 2nd gear at 65mph is NOT fun)

What is the IAS/AICV???? On the throttle body?? idle air stepper or whatever??

Think this is giving me issues in 4lo trying to apply just the right amount of steady throttle??

 

[southernrebel20]

Mine idles well, I replaced the idle speed adjuster not long ago. It bounces a little, but nothing spectacular. How would you adjust/check adjustment on a the TPS?

 

[Brett M]

Mine idles well, I replaced the idle speed adjuster not long ago. It bounces a little, but nothing spectacular. How would you adjust/check adjustment on a the TPS?

You can check it's voltage to make sure it's within specification. There are a bunch of thread's on here....quick search should give you what you need.

 

[RichP]

Back a couple of years ago I had to have a remanufactured engine put in my 98 5 speed XJ. After it was in I had a hesitation almost all the time, I tuned it up, cleaned the TB, tested the sensors with the snapon modis tool and never found the cause. It drove my buddy the mechanic who did it nuts for 2 years. Last January the alternator went and I had to order and install a new one, I replaced it with a Nippon Denso [the expensive one] and it ran fine after that.
I came to a couple of conclusions, one, when they replaced the engine they let it run in the shop hooked to a exhaust gas exhaust system and did not drive it till they got everything done and buttoned up, result was the ECU 'learned' it's parameter IDLING in the shop for 30 minutes. When the alt went they disconnected the battery, removed the alt and let it sit overnite till the part came in, the replaced it and it ran for 5 minutes then I took it out for a 40 minute drive then went home with it. It ran and still does without any hesitation anymore.
Two, the alt was going bad over that two years and it finally took the alt fully dying and getting replaced to solve the problem.
Personally I think that it's a good idea to disconnect the battery every couple of years and let the system relearn it's parameters.

 

[Timber]

Personally I think that it's a good idea to disconnect the battery every couple of years and let the system relearn it's parameters.

I completely agree (partly because I do just that).

 

[99SJ_Ex]

To bring an ooold forum back to life, I found a little piece of information that might give us an idea to try... A while back, there was a TSP out for 1999 Grand Cherokee's that had what they called a "Cold Start Hesitation/Cold Restart Hesitation" In it they explain that when first started, the 02 sensors prematurely go into close loop. What they did to fix this was re-flashing the PCM/ECM with the DRB III. There is an "updated" software that apparently takes care of the problem.... Now heres the interesting part.... According to several people I talked to, In this time frame Chrystler/Jeep was using the same power trains in both Cherokee and Grand Cherokee vehicles. This we all know. So My theory is to re flash the ECM/PCM and see if this does in fact fix the problem. Any other ideas of late? Im still investigating....

Austin

 

[RichP]

To bring an ooold forum back to life, I found a little piece of information that might give us an idea to try... A while back, there was a TSP out for 1999 Grand Cherokee's that had what they called a "Cold Start Hesitation/Cold Restart Hesitation" In it they explain that when first started, the 02 sensors prematurely go into close loop. What they did to fix this was re-flashing the PCM/ECM with the DRB III. There is an "updated" software that apparently takes care of the problem.... Now heres the interesting part.... According to several people I talked to, In this time frame Chrystler/Jeep was using the same power trains in both Cherokee and Grand Cherokee vehicles. This we all know. So My theory is to re flash the ECM/PCM and see if this does in fact fix the problem. Any other ideas of late? Im still investigating....

Austin

When I programmed our 97ZJ with the chrysler scan tool to add a new keyfob for the alarm and door locks the first thing I saw on the first screen 'ECM ID 98XJ Jeep'.. not ZJ, XJ.
I'm actually dickering with a guy who has a 98ZJ with a blown re42 tranny, 4.0, 242. If I can get the money together I'm picking it up and converting it to a 5 speed with a 98XJ 5 speed ecu. I have the clutch hanger and other parts for the conversion except for a 5 speed but until I get the ZJ I'm not coughing up for that unless one falls in my lap somehow. If you look at any ZJ you will see the stamped cut out for the clutch master cylinder on the firewall and the mount points for a clutch pedal under the dash, they actually made them for 2 years as an option, I found one in a junk yard and grabbed all the parts I could.

 

[99SJ_Ex]

Well I actually had my jeep throw a cyl#1 Misfire this moring because the engine was sagging soo bad... Im running out of ideas here...

Austin

 

[danblue636]

I'll bet you are having a little bit of a hard starting problem too...? My '99 does this too only after sitting all night though. The fuel pump bleeding off fuel pressure problem that you hear so much about is the problem.

 

[Monkey55]

Just for the record, I'm having the same exact problem with my '99.

It only does it when it's been sitting and is cold. It only does it for the first 20 to 30 feet under 20mph. It idles fine cold and hot. When I'm accelerating, it will stop accelerating and keep a constant speed for a few moments, then start picking up speed again.

It has a completely new exhaust system including cat and o2 sensors, new plugs, wire, and rotor. Fuel pressure at the fuel rail tested ok too.

I was starting to think the torque converter too, but I think I'm going to either have the computer flashed or find someone who has one of those expensive scan tools. It starts up fine every time.

:banghead:

E

 

[searchingforXJ]

My 99 does a similar thing too. It's hardly noticeable but it's there.

 

[pkinkel]

I'm in the same boat as well with my 98. I'm throwing a code for an 02 sensor but 2 new Bosch sensors have not cured it. I haven't lost any gas milelage or anything like that. It only happens after it has been sitting and happens once and never again for the rest of the day at least. I do have a crack in my header at the "Y" it could have something to do with it as well.

For those of you who are having power loss during acceleration and throwing codes for the o2 sensor I may be able to make a contribution. I have a '98 and my "check engine" light came on so I scanned and found out it was for the o2 sensor. Around the same time I noticed a large hesitation when trying to accelerate and I could feel in my gas pedal what seemed to be a bump followed by what sounded like a small backfire. I replaced the o2 sensor and still threw codes. It ends up I had a leak in my T-case and it sprayed oil on my wiring harness; the fluid corroded the insulative wire sheaths and shorted them out. I replaced the wiring to my o2 sensor and now my XJ runs great. Since the o2 sensor monitors the rich/lean mixture I was shorting out and my ECU told my engine to enrich my air/fuel mixture causing a stumble on acceleration. Obviously many engine problems can give you an "02 sensor" code including a dirty intake, bad injectors, low fuel pressure, vacuum leaks etc. Mine happened to be a small wiring problem; just hoping to save someone the headache I went through figuring this out.

 

[Monkey55]

Thanks for the info pkinkel. Even though some of us don't get any error codes, that could be a possibility.

btw - Welcome.. This is your first post after joining in Aug of '07..

E

 

[seanof30306@yahoo.]

96 XJ Up Country

While mine is a '96, it was one of the last ones built, and I'm pretty sure it has a '97 engine/pcm; the TPS, IAC, etc. I've put on it all ended up being '97 parts, not '96.

I have something very similar to what is described above that only happens every once in a great while, and only on cold starts. It has a hesitation a few seconds after I start off, it pops back through the throttle body once or twice, then clears up. One time this summer, on a 150 degree day with the AC running, it did it much worse than normal, after it had been running for awhile, and persisted for awhile instead of clearing up right away. I eventually booted the throttle a few times, and it cleared up.

It had another problem that may, or may not have been related. I was experimenting with hypermiling, and was coasting with the engine off, shutting it off at stoplights, drive throughs, etc. Shortly after I started doing that, though, the converter began unlocking and relocking while cruising, so I quit coasting with the engine off, assuming that was "confusing" the VSS. The converter problem cleared up.

I kept shutting it off at lights and drive throughs, though. It began giving me trouble on restarts, only doing so if I would floor it, and running poorly for awhile after that.

I reset the pcm, no change. Dit it again, no change. Dit it a third time, and the problem cleared up.

It didn't change the occasional cold start hesitation/popping, though. It still does it.

 

[Ecomike]

96 XJ Up Country

While mine is a '96, it was one of the last ones built, and I'm pretty sure it has a '97 engine/pcm; the TPS, IAC, etc. I've put on it all ended up being '97 parts, not '96.

I have something very similar to what is described above that only happens every once in a great while, and only on cold starts. It has a hesitation a few seconds after I start off, it pops back through the throttle body once or twice, then clears up. One time this summer, on a 150 degree day with the AC running, it did it much worse than normal, after it had been running for awhile, and persisted for awhile instead of clearing up right away. I eventually booted the throttle a few times, and it cleared up.

It had another problem that may, or may not have been related. I was experimenting with hypermiling, and was coasting with the engine off, shutting it off at stoplights, drive throughs, etc. Shortly after I started doing that, though, the converter began unlocking and relocking while cruising, so I quit coasting with the engine off, assuming that was "confusing" the VSS. The converter problem cleared up.

I kept shutting it off at lights and drive throughs, though. It began giving me trouble on restarts, only doing so if I would floor it, and running poorly for awhile after that.

I reset the pcm, no change. Dit it again, no change. Dit it a third time, and the problem cleared up.

It didn't change the occasional cold start hesitation/popping, though. It still does it.

While some of your problem was caused by confusing the ECU with the engine off deal, it also sounds like you may have a leaky fuel injector!!!!!

 

[mjma]

Update!!

99 XJ, had hesitation on cold starts that started on acceleration about 100 yards down the road, regardless of how long it idled. Wasn't that bad of an issue like that, but in 4low, it would sometimes (more often that I wanted it to) cough at certain throttle positions and not run smooth when I wanted to keep the throttle at just a tad over idle...which is key for crawling!! It was a problem!!

Also worth mentioning I throw a front 02 sensor code....and it's a new universal cat (don't ever buy one!!). Not too interested in getting another new one...so whatever.

So, I picked up a used TPS (I know this is probably a stupid idea, but it was 2 bux) at at junkyard to see if it was indeed the TPS. I threw it in the other day and afterwards it seemed to me like the hesitation got worse!! Longer duration and more of a loss of power even after the hesitiation was gone!! Well, that was a week or so ago, and now it's fine!! No more hesistation after cold startups and the throttle will stay as smooth as my foot can make it go in 4low!!!

While I don't think anyone would recommend a junkyard TPS....it seems to have worked for me!!

 

[Ecomike]

Update!!

99 XJ, had hesitation on cold starts that started on acceleration about 100 yards down the road, regardless of how long it idled. Wasn't that bad of an issue like that, but in 4low, it would sometimes (more often that I wanted it to) cough at certain throttle positions and not run smooth when I wanted to keep the throttle at just a tad over idle...which is key for crawling!! It was a problem!!

Also worth mentioning I throw a front 02 sensor code....and it's a new universal cat (don't ever buy one!!). Not too interested in getting another new one...so whatever.

So, I picked up a used TPS (I know this is probably a stupid idea, but it was 2 bux) at at junkyard to see if it was indeed the TPS. I threw it in the other day and afterwards it seemed to me like the hesitation got worse!! Longer duration and more of a loss of power even after the hesitiation was gone!! Well, that was a week or so ago, and now it's fine!! No more hesistation after cold startups and the throttle will stay as smooth as my foot can make it go in 4low!!!

While I don't think anyone would recommend a junkyard TPS....it seems to have worked for me!!

The delay in the return normal operation after changing the TPS was probably due to the ECU/PCM (and TCU if automatic) having old stored data on the old TPS min, max, ... readings. Battery disconect to clear the old data values does help when replacing bad sensor parts. It will eventually over write old data with new data in the ECU, but makes you wait to see if the fix is really a fix. A scanner to clear the battery disconnect code helps too.

 

[mjma]

I had a feeling it must have been due to old stored data or something! After my intial two tests (two days apart) I was bummed, and thought that I'd run it for a while and then change it back, but then it went away!

 

[CartsXJ]

My 98 does the samething and I write it off to the pressure valve on the fuel pump failing. Unfortunately, when jeep went away from the full loop fuel system, gas get trapped in the rail and is allow to expand turning into vapor. There also might be a light leak on the fuel rail, allowing the pressure to be taking off the fuel rail; allowing the residual heat to heat up and expand the fuel to a vapor. Then when you hit the as the vapor is pushed thru the injectors and causes hesistation.

I get a CEL light.........mis-fire on Cylinder 6.

Ive already replaced the fuel pump assembly once and it cured it, but its reared its ugly head again. I've noticed it more since switching to the late model 99 intake manifold. I might look into the heat sheilding of the fuel rail and injectors along with hood vents to allow heat to escape. Heck, I've even looked into some how switching to an earlier fuel rail with a full loop fuel system, allow fresh fuel to circulate.

But these are my theories, I have a feeling that everyone issues are different. If anyone has it really figured out on the late models, I would love to find out.

 

[1968 Charger B5]

I have the exact same problem with my 98 with 108,000 miles. I changed the entire exhaust system and did not solve the problem. I am guessing the crank position sensor, seeing it shoul dbe changed around 100k miles anyway. Next I'll be going for the tps. I did not change the 02 sensors though,...had throwing money around.....but it is so fucking annoying...