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Old 06-16-2011, 07:50 PM   #1
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REALLY bad idle vibrations

ok well i have been having minor rough idle issues and i have been replacing parts that could be the issue... i drove my jeep to work this morning and it was fine. on my lunch i changed the IAC on the throttle body, the idle vibration is terrible now, i mean i am shaking in the cabin. the RPM is normal when in idle and the engine really isnt physically shaking like the vibs i am feeling in the cabin. so i went home and on my way i noticed a knocking noise coming from the transfer case, only in idle. when i got home a put the old IAC back in to see if it will fix the problem but it didnt. now if the RPMs are at 1 or above the vibs arent there and arent there when im driving, just idle. i gave my vac lines a quick look and they are all intact. but i dont understand why my TC is knocking when im idle.... any ideas anyone??

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Old 06-16-2011, 08:01 PM   #2
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You sure it isn't the tranny? Throwout bearings are known to rattle at idle with the clutch out. The tfer case isn't doing anything at idle... Unless a bolt is loose and it's just rattling because the truck is shaking.

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Old 06-16-2011, 08:06 PM   #3
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You sure it isn't the tranny? Throwout bearings are known to rattle at idle with the clutch out. The tfer case isn't doing anything at idle... Unless a bolt is loose and it's just rattling because the truck is shaking.

would it rattle with the clutch pedal pushed down and released? or does it not really matter? could it be the front driveshaft U-joint?
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Old 06-16-2011, 08:55 PM   #4
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anybody?
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Old 06-16-2011, 09:05 PM   #5
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At idle the u-joints shouldn't be moving either. I'd say leave it in neutral, clutch out, e-brake on, and crawl under there. See if you can tell exactly where that knock is coming from. If it's hard to get direction on the sound, try putting your hand flat on the transmission, tfer case, oil pan, etc... You should feel the knock strongest from the part causing it.

Can you describe it a bit more? Does it increase/decrease frequency exactly with engine revs? Is it unmuffled metal on metal, or does it sound like it's under oil? Does it go away or change if you move the tfer case into N, 4H, or 4L? Does it change pitch/frequency if you press clutch in/out? How about if you move through the gears with the clutch pressed in? What if you drag the clutch just enough to make a bit of contact for a second, but don't take off or give it gas?
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Old 06-16-2011, 09:19 PM   #6
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it is an on and off knocking... it isnt constant.. it is knocking when in idle... not knocking during RPMs over 1 and shifting through gears... havent tried putting in 4WD... it sounds like a hammer tapping on metal... it happens in idle whether i have the clutched pressed in or i am in neutral.... havent tried the last suggestion... but the cabin vibration is like an earthquake and then the knocking occurs
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Old 06-17-2011, 07:24 AM   #7
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ok well this morning i started it up and the vibs were still there along with the knocking noise. on my drive it work it continued for a good 8 miles or so... i heard this metal chattering noise a couple times when i was at a complete stop and if i was cruising, say 30 + mph and then push the clutch pedal in to downshift/slow down i would here a odd noise. it has a metal chattering noise to it but it only lasts a second or two. kinda sounds like exhaust release to me but im not sure. anyways the last couple miles to work it started to calm down a bit... dont know why or how but it did. it shifts perfect and the clutch feels fine to me. so needless to say i am lost lol.
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Old 06-17-2011, 07:40 AM   #8
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have to pinpoint the area the noise is coming from. front/back of engine? front/back of trans? front/back of case? etc... And if it does it sitting still, its not going to be u-joints like mentioned.

Have you done the basic tune up stuff that is designed to fail? Dist. cap, rotor, spark plugs???
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Old 06-17-2011, 07:51 AM   #9
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have to pinpoint the area the noise is coming from. front/back of engine? front/back of trans? front/back of case? etc... And if it does it sitting still, its not going to be u-joints like mentioned.

Have you done the basic tune up stuff that is designed to fail? Dist. cap, rotor, spark plugs???

its definitely not coming from the engine at all. im going to have to feel around both the TC and Trans to tell for sure which one it is coming from from... my guess is Trans because i am in 2WD 99% of the time.

yup i have done wires, plugs, cap, rotor and air filter. changed the TC and Trans fluid last fall/winter. i also changed the cat, muffler and tail pipe. got a mechanice to drille out the back exhaust manifold bolt and put a gasket on. i have changed the thermostat and TPS.

as far i know, from the PO, the clutch has never been replaced and i currently have 116,400 original miles on the jeep.
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Old 06-17-2011, 08:03 AM   #10
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Ooohhhh, you had the distributor apart? Any chance you put it back together at a slightly different angle? Getting the ignition timing a few degrees too early would make for a pretty rough idle at low revs, that would clear up once the engine gets up to speed.
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Old 06-17-2011, 08:28 AM   #11
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Ooohhhh, you had the distributor apart? Any chance you put it back together at a slightly different angle? Getting the ignition timing a few degrees too early would make for a pretty rough idle at low revs, that would clear up once the engine gets up to speed.

yeah i did. alls i did was replace the rotor, which only goes on one way if i remember correctly, and the cap... i double check it at lunch if it isnt raining. but i did this months ago...
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Old 06-17-2011, 01:31 PM   #12
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I have the same exact issue (except for the metal sound you hear) its just a horrible idle below 1k. I normally put my hand throttle at 1k so i dont have to feel the darn shacking. For me it got worse when i put brown dog 1inch lift motor mounts on and I have always figured it was just the vibs from the motor thru the frame. but that really doesnt make sense since it goes away with a higher idle. Can a vac leak cause any part of this?
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Old 06-17-2011, 02:01 PM   #13
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I have the same exact issue (except for the metal sound you hear) its just a horrible idle below 1k. I normally put my hand throttle at 1k so i dont have to feel the darn shacking. For me it got worse when i put brown dog 1inch lift motor mounts on and I have always figured it was just the vibs from the motor thru the frame. but that really doesnt make sense since it goes away with a higher idle. Can a vac leak cause any part of this?
Did yours happen all of sudden? Yeah I'm thinking it could be a bad vac line somewhere... or maybe a bad spark plug/ wire
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Old 06-17-2011, 10:44 PM   #14
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ok well not sure if this is totally normal but when im at a stop in neutral, during idle i slightly turn then hold the steerring wheel and the rpms increase a little (which is normal with all power steering vechiles, correct?) but when i release the steering wheel the RPMs drop all the way down to the little line before the 0 and slowing goes back to normal RPMs. its like the engine is starving for air.
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Old 06-18-2011, 03:13 PM   #15
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how would i do the ignition timing? i have a inductive timing light
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Old 06-18-2011, 04:04 PM   #16
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nvm my manual says the they cant be adjust, its controlled by the PCM.\

could it be my camshaft postion sensor or MAP sensor?
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Old 06-19-2011, 06:02 PM   #17
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ok for whoever is watching me talk to myself i have some info... i had a hunch that it might be something with the fuel system so i went and pick up some lucas injector cleaner dumped it in the tank, got gas, and drove around for like 6 miles to get it through the fuel system and the earthquake vibs are gone! its back to mild vibs which is ok with me. but now i believe that part of fuel system is really really dirty.

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