Bucking, Sputtering, Wierd idle IAC motor, TPS, Im stumped?? - JeepForum.com
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Unread 06-01-2009, 08:56 PM   #1
jlcca844
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Bucking, Sputtering, Wierd idle IAC motor, TPS, Im stumped??

Ok to start i had another post on here about some problems with my jeep. Its a 98 jeep grand cherokee laredo 4x4 I6 4.0 engine. A few months ago i had some problems with my jeep bogging down and acting like it was starved for fuel almost anytime. It kept throwing a P0138 code, turns out it was the wiring on the wiring harness it has since been repaired. The probs stopped for a week or so and now they are back. My jeep started bogging down again and acting like it was out of fuel. It happens mostly now when i pull off from being stopped, not in park just sitting at idle. And really bad in hot weather. Yesterday when i was pulling off from a red light it started bucking and jerking again it hadnt done this in almost a week. Now while it is bucking, jerking, bogging down etc. i can feel and hear a clicking or wierd noise kind of like a clicking thump if that makes any sense lol that is underneath the gas pedal. Then when i let off the gas pedal for a minute it stopped and caught up, as it always does. Then drove fine the rest of the way home. Then last night i was sitting in a drive thru and all of a sudden my jeep started revving up on its own and my foot was on the brake but the jeep was trying to take off and kind of lurching forward. None of the other instruments in the dash panel change except the rpm when it either bogs down or revs up while im sitting at idle its always only the rpm that does anything. I have read that it is most likely the IAC or the TPS is this true. If so which one is it most likely to be?? I am so tired of trying to find the real problem it wont do it when anyone important that could tell me what is going on drives it. It is driving me crazy!!! I cant really go that far im too afraid that it will either take off on its own or not go fast enough and get me hit. What should i do??? Any help is greatly appreciated!!! Im lost at this problem


Last edited by jlcca844; 06-01-2009 at 08:59 PM.. Reason: forgot something
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Unread 06-01-2009, 09:11 PM   #2
Mickey_D
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Well, if you're having problems with it when you've got your foot at all on the gas pedal it rules the IAC out. Its name tells you why. Idle Air Control. It does nothing as soon as those throttle plates open.
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Unread 06-01-2009, 09:20 PM   #3
jlcca844
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Quote:
Originally Posted by Mickey_D View Post
Well, if you're having problems with it when you've got your foot at all on the gas pedal it rules the IAC out. Its name tells you why. Idle Air Control. It does nothing as soon as those throttle plates open.
thats what i thought but my mechanic friends say that could be one of the problems. i think that the downstream o2 sensor needs to be replaced but everyone kept saying that it wasnt the sensor, it was the wire harness. but even after it was fixed it threw the code once (the p0138) but hasnt since i had the codes cleared with that machine the week before last. it just messes up w/o the cel coming on. and the problem is intermittent. i just wonder if it could be a combo of both or all three. i could be wrong since i know nothing about cars, but why would it constantly throw that code if there isnt something wrong with it. i do have a minor exhaust leak that i know i need to get fixed.
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Unread 06-01-2009, 09:35 PM   #4
baxy
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sounds like a job for a mechanic with experience with jeeps and a good scan tool
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Unread 06-02-2009, 01:17 AM   #5
BlingBlingZJ
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it sounds like it could be the pcm.. try backing out the screws in the middle of the pcm and see if that helps.
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Unread 06-02-2009, 02:00 AM   #6
CB76
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Don't know if it helps, but I had a very similar problem with an '84 Ford F150, and it turned out to be a vacuum hose.
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Unread 06-02-2009, 07:14 AM   #7
jlcca844
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Originally Posted by BlingBlingZJ View Post
it sounds like it could be the pcm.. try backing out the screws in the middle of the pcm and see if that helps.
i have read about that before, and thought about doing it so i may try it for a few days and see what happens. my bf and my mechanic friends think i am crazy since it wont do anything when they drive it. i am tired of being told i am imagining things.
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Unread 06-02-2009, 10:00 AM   #8
4Slow9erHybrid
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Does this bucking etc happen shortly (2-3mins) after starting the engine and lasts only ~ 2mins? This might be due to an aging upstream (not the downstream) O2 sensor. It's easy to determine if it's indeed caused by the O2 sensor, just disconnect it. The connector is attached to one of the engine oil pan studs on the driver's side, approximately above the axle. The 4.0 engines seem to be effected quite often by this issue (ZJs and WJs). With the O2 disconnected you WILL get a Check Engine Light. Don't worry that won't cause any harm, just don't plan any 1000mi road trip with a disconnected O2 sensor. A few days of driving like that won't hurt anything. If the bucking goes away, you diagnosed a failing (aging) O2 sensor. Replace with MOPAR only (not Bosch!!!) or you'll have the same issue with a new one!!! Let us know if this solves your issue.
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Unread 06-02-2009, 10:14 AM   #9
jlcca844
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thanks for all of your help... i will get back with everyone and let you know what is going on with it.
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Unread 06-02-2009, 10:16 AM   #10
jlcca844
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Quote:
Originally Posted by guthycs View Post
Does this bucking etc happen shortly (2-3mins) after starting the engine and lasts only ~ 2mins? This might be due to an aging upstream (not the downstream) O2 sensor. It's easy to determine if it's indeed caused by the O2 sensor, just disconnect it. The connector is attached to one of the engine oil pan studs on the driver's side, approximately above the axle. The 4.0 engines seem to be effected quite often by this issue (ZJs and WJs). With the O2 disconnected you WILL get a Check Engine Light. Don't worry that won't cause any harm, just don't plan any 1000mi road trip with a disconnected O2 sensor. A few days of driving like that won't hurt anything. If the bucking goes away, you diagnosed a failing (aging) O2 sensor. Replace with MOPAR only (not Bosch!!!) or you'll have the same issue with a new one!!! Let us know if this solves your issue.
Yes it usually does i dont go too far out of town due to the probs it does do it other times also but not always usually its only after a few mins after i leave my house my boyfriend lives about 6 miles away and it does it about halfway to and from his house almost always when i come out of a stop at a stop sign or stop light. it doesnt do it for a whole two mins. if i let off the gas pedal it will slowly stop sputtering and get back to normal but if i keep pushing the gas pedal nothing changes and it wont go any faster than 10-15 mph. a while back the only time it did it to my bf he said he could push the gas pedal all the way to the floor while it was bucking, sputtering etc. and not going but 10 mph. he says its the fuel pump, but everyone keeps saying the pump either works or it doesnt there is no in between
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Unread 06-02-2009, 10:21 AM   #11
4Slow9erHybrid
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Quote:
Originally Posted by jlcca844 View Post
Yes it usually does i dont go too far out of town due to the probs it does do it other times also but not always usually its only after a few mins after i leave my house my boyfriend lives about 6 miles away and it does it about halfway to and from his house almost always when i come out of a stop at a stop sign or stop light. it doesnt do it for a whole two mins. if i let off the gas pedal it will slowly stop sputtering and get back to normal but if i keep pushing the gas pedal nothing changes and it wont go any faster than 10-15 mph. a while back the only time it did it to my bf he said he could push the gas pedal all the way to the floor while it was bucking, sputtering etc. and not going but 10 mph. he says its the fuel pump, but everyone keeps saying the pump either works or it doesnt there is no in between
Exact symptoms of a failing O2 sensor. For some reason it seems to affect the 4.0 Jeeps only. This should be in the FAQ section. Just crawl under the Jeep and disconnect that sensor. The O2 sensor is screwed into the exhaust pipe, just follow the wires and you'll find the sensor. Make sure the disconnected wires don't get caught on the driveshaft etc.
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Unread 06-02-2009, 10:32 AM   #12
jlcca844
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Quote:
Originally Posted by guthycs View Post
Exact symptoms of a failing O2 sensor. For some reason it seems to affect the 4.0 Jeeps only. This should be in the FAQ section. Just crawl under the Jeep and disconnect that sensor. The O2 sensor is screwed into the exhaust pipe, just follow the wires and you'll find the sensor. Make sure the disconnected wires don't get caught on the driveshaft etc.
thanks i will try this and post in a couple days after i have driven it. i have thought all along that it had something to do with the oxygen sensors but all the people i know kept telling me thats not it. but like i told them why would it keep throwing a code for it if it had nothing to do with it that is the ONLY code that it has thrown in the past few months...never anything else. So i hope soon i can tell them I Told You So lol. Thanks so much!!!
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Unread 06-02-2009, 12:37 PM   #13
4Slow9erHybrid
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Quote:
Originally Posted by jlcca844 View Post
thanks i will try this and post in a couple days after i have driven it. i have thought all along that it had something to do with the oxygen sensors but all the people i know kept telling me thats not it. but like i told them why would it keep throwing a code for it if it had nothing to do with it that is the ONLY code that it has thrown in the past few months...never anything else. So i hope soon i can tell them I Told You So lol. Thanks so much!!!
Mine wasn't throwing any codes. That was the most frustrating part. I suspected a tranny issue first.
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Unread 06-02-2009, 12:52 PM   #14
Mickey_D
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Also as a side note, fuel pumps CAN degrade without completely failing. I haven't had experience with it in a Jeep, but I have had it happen three times with Chevrolet. And considering it's the same company that makes the fuel pumps for both...
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Unread 06-02-2009, 04:15 PM   #15
jlcca844
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Originally Posted by Mickey_D View Post
Also as a side note, fuel pumps CAN degrade without completely failing. I haven't had experience with it in a Jeep, but I have had it happen three times with Chevrolet. And considering it's the same company that makes the fuel pumps for both...
thats what my bf said and i have a friend whose wife drives nothing but jeep and he said that hers did the same thing only hers died a lot quicker. i may have them pull off the gas tank and check the fuel pump and make sure its ok as well as check the tps, iac valve, and both o2 sensors. i figure that i am bound to find it. and alldata has helped me quite a bit. it just that so many probs have the same symtoms and its hard to pinpoint the acutal prob causing the conditions i am having. thats what is sooooo confusing.
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