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Old 02-14-2011, 06:54 PM   #1
Join Date: Oct 2009
Posts: 8
Question mid range engine shimmy

hey Jeep experts,

Engine was running a lil heavier than normal a few months ago so i thought i'd do the cheap (and Lazy) thing and try some marvel mystery oil to hopefully improve mpg and (hopefully) degunk. The first time bottle I used was fabulous, the engine ran stronger than ever since i've had it, and got better mpg. After completing the first bottle and just using 87 gas for the next few months, recently it started to get a little sluggish again.tried another bottle but it hasn't really seemed to help... now it runs great in high torque, but at mid ranges depending on the gears, about 15 -25 k rpms there is a sharp reverberation. I did some research, saw others with similar problems and checked the plugs, which apparently read running rich, (makes sense adding the mystery oil right)and they were the bosch premium platinum, (previous owner, I bought in 2003.) So i pulled em and put in USA champion copper plugs, test drive... a little better, but, unfortunately shimmy is still there at the mid range Rpms. Where to look next?

BTW...Eye and hand inspection of vac lines seems to be ok without a system integrity check. Any guesses? best? worse case scenarios. Okay experts, a gimme yer advice and DIY info!!!


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Old 02-14-2011, 10:54 PM   #2
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mas info

okay just in case it matters, 92 yj, stock, 4.0...
Damn no responses??? LOL Anyone care to take a semi- educated guess?
All experience levels welcome to answer..... got some time off and wanna attack it. Thanks. No seriously...Buehler? Thanks.

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Old 02-15-2011, 04:32 PM   #3
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Though cleaning the throttle body wouldn't hurt, the articles i've read mostly regard idle problems, but could the build up also have an impact on mid range power, and the engine shimmy i spoke of above?
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Old 02-17-2011, 06:38 PM   #4
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okay so i picked up some sea foam and did some further inspecting around under the hood, and think i've identified some potential areas of concern. On the top of the engine they're two valves both of which need to be replaced, or at least the gaskets surrounding them, as well as one of the hoses needs has a coupling that i replaced as it was unsealed. I used the sea foam to clean out the throttle body and wow wonders! On the test drive afterwords felt better acceleration and smoother engine running and less noise in off the egnigne but I still get a little of the vibrations just at different rpms now, so I'm gonna hit it from both angles again and hopefully cure it up. That is more cleaning of the throttle Body, and re-attack the vacuum and vent lines to make sure the gurgling and jerking aren't caused by burps in the systems integrity. Btw also cleaned out the idle air bypass or whatever its called above the air intake butterfly, and idles much better. Thanks Wrangler Forum for all the threads and great advice from all those guys out there with some cash and fortitude I know I'll get er done!
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Old 02-17-2011, 07:25 PM   #5
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All mounts okay? Engine, trannsmission, etc.
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Old 02-19-2011, 05:50 PM   #6
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Billytheyj; I think so, it doesn't seem like the torque is pushing the engine or tranny over at all, I sprayed the throttle bdy with more sea foam today, and foollwed those procedures, and it seemed pretty good, almost non existent. I put more gas in (arco 87) and afterwords felt it again, but only momentarily. right now I am thinking two things;i must have a vaccum leak that i haven't been able to locate, or the throttle body etc, must be gunked pretty bad...I've only used one bottle to clean it, being the first and only time since I've owned it in 9 years, and maybe 20,000 miles. Who knows about the previous owners, But by looking inside the butterfly valve, its pretty pretty dark, and i don't think i'm going to get it sparkling or anything without going the other nine yards, disassembling, and thoroughly cleaning as other threads have suggested, and while that would definitely have its benefits and reduce the possibilities/ as far as problem shooting goes, I'm not prepared to do that just yet. I guess I'll have to look sharply at finding vacuum leaks. Any suggestions? common hidden places where vacuum lines fail or crack? and If the seals around the pcv valves are loose ( not air tight, but a little wiggle room) Do you think it would be enough of a loss of system integrity to cause juttering? Thanks.
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Old 03-04-2011, 08:26 PM   #7
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Okay been a while since i reported back, but here goes...

I used the spray seafoam product, de gunk or sumpin which according to the website I shot down at the butterfly flap away from the idle air flow hole (which By the way I cleaned out while off with a flat head, careful to pull the gunk away from the main throttle body by being nifty and twisting the flat blade just so to only knock off the gunk while pulling the driver blade out) Which i must attest had an immediate impact on the idle performance as mentioned above. If I repeat A bit, tfb. lol It's my write up!

Better description of the problem? okay
There has been (still) dragging, or pulling sense on the engine when i get to 20 rpms in second 25 in 3rd, and about 30-35 in 4th. its like the engine is smooth revving up to a certain point and then suddenly gets rough, and not only sounds rough but vibrates all the way through the dash. also , feel it slightly when letting off the accelerator after torquing through a turn or say going from first to third at consecutive stop signs.

okay so i got a can of the normal bottled sea foam, but decided that shouldn't couldn't wouldn't do the job alone without getting in and checking sh*t out. Not that hard Right? So i started with the vacuum lines *(again) and made sure tit wasn't the light or me rushing that missed something. Next i checked connections from vacuum lines to the throttle body. BINGO!!! the front valve running from the engine cover to the throttle body was caked in so thoroughly that i could not even poke a toothpick through it! I cleaned it thoroughly with some left over sea foam spray, toothpicks and yeah even a couple of q-tips soaked in the seafoam which cut right through the gunk.
checked the rear valve/ line/ connector too, first,( actually )which was pretty damn clean i was glad. Working my way forward, on the throttle body i checked a three way connector, which was clean. and with daylight subsiding, i made sure everything was back in its rightful and secured place. and started her up.

Pretty good, i'd say but still not quite right....so more sea foam, this time the actual pour in bottle ( not the spary can) and i followed the instructions from other write ups using it, pouring in about half (actually more like a third, at Jeeps normal running temperature) while running and getting it to bog out a bit, after a few times a so, i turned it off and poured in about another third of the bottle, and waited 5-7-10 min before starting her up, at which point the smoke cloud finally shut my neighbors dog up! j/k...anyway, I ran it for about five minutes before the exhaust cloud finally simmered down to a tolerable and non lethal level, and shut her down.

Today on a short test drive I felt significantly less pull and vibrations, and overall better response.

The what?
I'm guessing that using the Marvel Mystery Oil knocked off some rather large deposits within the throttle body or actually the vacuum line or even the casing ( i used some in the oil as well as the gas) and with the heat and recurring deposits solidified the already gummed up line/ connector valve to the throttle body just dumping more gunk on more gunk and suffocating the line for what ever it did... while I am not sure that the problem is "completely solved" by only taking a short short road test.I am happy at this point that it seems much better. In fact like above i am certain that the Seafoam further leaned the throttle body and around the rings and what not becasue the overal response seems better and feels smoother....

I gotta Say... I love My 4.0!!! What would it be like with one of the bigger conversions??? ****** I can only imagine!
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Old 03-13-2011, 05:37 PM   #8
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Damn I'm back, and unhappy to report the problem isn't fixed.
Fuel Fire and Air...Right? I think the problem's got to be air or fuel.. ha ha since i've already changed out the sparkplugs... I am about to remove and clean the throttle body.. the AIS motor, and..not being a mechanic by trade, I had assumed the entire system south and connecting to the main engine was the throttle body, and had considered taking it all off and making sure to clean it thoroughly to help the flow of gas and air...not just the throttle body, is there any danger's i should specifically be careful of that isn't obvious from looking at it from above?

I have checked all the lines and see no breakages or disconnected lines, but the problem still persists when when i rev up to a certain point before shift, and at the same point when either in a gear with out accelerating...

Is it possible the problem could be as simple as a blockage in the fuel line, a fouled up fuel filter? or even a less than optimal fuel pump?

the problem really doesn't happen when idling, shifting, or when it's out of gear...perhaps because of the the workload on the engine/transmission... which leads me to think at such a middle range of torque the gas/air mixture isn't stout enough to prevent the engine from gurgling/stuttering...but the thing that's weird is it doesn't necessarily feel like its losing power, just struggles through that range, until I either shift out of it, or accelerate beyond it...

Man I would really like someone else's opinion on this... tI'm going to start with the simplest and move progressively towards the more work cost abrasive solution... if i've missed something or erred in my thought process i'd appreciate being corrected, and any additional possibilities, opinions and oversights... thanks for your time, interest and thoughts....
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Old 03-14-2011, 01:25 AM   #9
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Posts: 8
Thumbs up

okay... so ntoday i remeoved the thorttle body complely and leaed every inch of it including the arm from the AIS motor.. ... let me say at this moment( because who knows what temteraturea and whteher might bring) it has been brilliant! I removed at least 1 but probably two milimeters of depositis off of the inside of the throttle body.. who knew it had a graduated curve/concave symmetry?wo.. i'm enven less concerned with my spelling now that i've got some results...who gnows maybe nsst time I might eben get some replonces? good luck watcheva yo deal...latz...relic

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mid range rpms , rough running , vibrations

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