99 Cherokee hesitation/cutting out????

Hi everyone, I'm new to the site. I just recently picked up a 99 Cherokee with 34k miles on it. I have been having some hesitation problems with it at low engine rpms. when taking off from a stop, shortly after taking off it will cut out a little bit or hesitate, but if you put your foot in the peddle a bit more, it seems to correct itself and run normal. I just replaced the plugs, plug wires, cap/rotor, O2 sensors and it was running much better. I think some of the problem was the older wires were arching on the block. It was running good (for the few miles to my office from the shop) and then I noticed it hesitating again. Does anyone have any ideas? Fuel pump? Fuel filter? I don't know what else to do at this point.

Does anyone have any suggestions? I'm new to Jeeps so I'm not too familiar with the 4.0L.

Thanks in advance for any help you can offer.

-Chris

Sounds exactly like what my '99 does when the battery is drained. If my battery dies and I get a jump start, I have to maintain my RPM's for awhile before it will idle on its own or drive normally again. Each time I slow down, it starts sputtering and shaking unless I keep one foot on the gas and one on the brakes as I come to a stop.

Coolant temperture sensor on the thermostat housing. My 99 was having a acceleration misfire or hesitation and I did all the same things you tried. It finally sent a Check Engine Light with a code for low voaltage from the coolant sensor. Put in a new sensor and it runs great.

The battery is actually new so I don't think it's that. I know it is not drained either because it cranks over very fast when starting.

it's odd because it only happens when it's cold. I have only driven a few miles since i replaced everything, but so far it's only when it's cold. Going to be driving it about 60 miles today so we'll see what happens on that drive. think a problem with an injector?

That is an odd problem. Sometimes after I have been driving my '99 and I shut if off, and I go back outside and and go to drive somewhere, it seems to cut out a little bit, but goes away if I give it more gas too. But it only does it after starting it up after it has been sitting for a few minutes. I don't know if this is the same problem, but mine is due for a tune up. I should probably take care of that and see if the hesitation goes away. I'll keep an eye on this thread and see if someone comes up with a magic answer.

I too have a hot restart problem on my 99. It has to sit for about 10 min after driving for a while ,I start it back up when I go to take off the first time it starts to hesitate I can give it more gas or better yet I let off the gas for a sec. and then it drives fine. I'm thinking it might be a tps going bad but I never looked into it.

fyrfytr1717 said:

Sounds exactly like what my '99 does when the battery is drained. If my battery dies and I get a jump start, I have to maintain my RPM's for awhile before it will idle on its own or drive normally again. Each time I slow down, it starts sputtering and shaking unless I keep one foot on the gas and one on the brakes as I come to a stop.

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Try cleaning the throttle body. I'm sure you're going to find out that it has a lot of carbon build up in it. The Idle air motor can only open up so far. Every time the battery goes dead the ecm goes back to a default setting and it has to relearn where it has to be. I see a lot of people coming in the shop for that problem.

Mike

After thinking things through and discussing with my mechanic, we are thinking it is the O2 sensor after the cat. when i put the new ones in, that is the one that seemed to be a little different than the one i pulled out. it fit fine, but the plug didn't have the "nub" on it to attach to the mount underneath the vehicle. The mechanic thought the same as he had a similar problem with another car in the recent past and the new O2 sensor fixed it. It's very possible I put the wrong one in. I'll let you know the verdict tomorrow.

I have a 99 also that does the same thing! After a warm start it seems to hesitate off of idle until it gets more gas. No codes yet though. 141K on the clock.

Z71456 said:

After thinking things through and discussing with my mechanic, we are thinking it is the O2 sensor after the cat. when i put the new ones in, that is the one that seemed to be a little different than the one i pulled out. it fit fine, but the plug didn't have the "nub" on it to attach to the mount underneath the vehicle. The mechanic thought the same as he had a similar problem with another car in the recent past and the new O2 sensor fixed it. It's very possible I put the wrong one in. I'll let you know the verdict tomorrow.

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The downstream o2 sensor should not effect drivability. The only thing it does is monitor the function of the cat, and make sure it is working properly. You can completely disconnect that o2 sensor and it will drive just fine, but throw a couple codes.

I had the same issues with my 97 about two years ago. Replaced the Cat, O2 sensors, blah blah blah... Still same issue. I put up a post on another forum and got advice on cleaning my PCM connectors. It worked for me. Have not had problems since (knock on wood).

Here is that thread I put up:

http://www.ilovejeeps.com/forums/showthread.php?t=17188&highlight=rough+idle

Hope it helps.

i recently had some terrible drivability issues and it all stemmed back to bad harness ground connections, especially the engine-to-firewall strap.. one of the worst months of my life figuring that one out..

There is a technical service bulletin for an engine misfire (hot engine only) on I believe the #3 cylinder. The fix involves installation of a heat shield around the fuel injector. Use the search function for more information about this. If I remember right, the fix kit from Jeep was under 10 bucks.

But as the original poster's problem is cold only, that won't fix his issue. I agree that the coolant temp sensor could be suspect here. Cleaning of throttle body never hurts. The after cat 02 sensor won't fix this one.

This might be a stupid question, I feel stupid for asking it, but I don't know the answer.

How do you clean the throttle body? Do you just dis assemble and clean? Or is there something special that someone should know? I tried to search on this but couldn't find anything.

To clean the throttle take off the air inlet tube. Get yourself some Carb spray, a few rags, and maybe a tooth brush. With the engine off and cool spray into the throttle body to get the carbon to soften up then use the rags and/ or tooth brush to clean the throttle body and the throttle blade.

There is some spray that they make that is just for throttle body cleaning. You have the engine running and hold the idle up around 1500 and just spray it in and wash all the carbon out. You could do that with carb spray but the carb spray is not to O2 sensor friendly. The Throttle body cleaner is.

Mike

Ok so I'm totally stumped and so is my mechanic. It finally threw O2 sensor codes last week so I changed them both out with factory Chrysler sensors and returned the Pep Boys ones I got. After all of that, it is still hesitating at low rpms when it is cold. I took it back to the shop and they have been checking every sensor and every connection. At the end of the day, they finally gave up and told me they didn't know what was going on. He suggested that it might be the computer, but he isn't certain. When they checked the voltage at the O2 sensors, they would read up and down. I guess they would go up to 8 volts and then back to 4. They checked the connections on the PCM, grounds, TPS, everything. I don't know what else to do. He said the dealer would have a tool that can test the PCM fully. Should I just buy one online for $200 or take it to the dealer? If I take it to the dealer, they will charge me $120 just to diagnose it.

Any thoughts anyone?????

So the dealer finally found out the problem. After going to one dealer already and an independent shop, the 2nd dealer was finally able to pinpoint the problem. Apparently the O2 sensor heater circuit was bad. They traced it back to it's own fuse and sure enough, the fuse was blown. The service writer, who was very knowledgeable, had never even heard of such a thing. I did drive it home and wow, what a difference. It drives great and this headache is over (hopefully).

Just thought I'd post this resolution to my problem in case anyone else was following it.

Thanks,

CB