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Unread 12-13-2010, 10:20 PM   #1
outlaw30
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High idle coming to a stop

'01 WJ, 4.7L, Quadratrac II, 120k.

Trans and TC seem to be working just fine, smooth shifts, normally idles just fine (I have a P0740 Torque Convt lockup light coming on, but only when I try to accelerate hard from highway speeds, so I don't think the issue is linked).

Problem is, when slowing down and stopping, idle is very high, around 900-1000. Trans shifts down to first with a lunge just as I stop, then after a few seconds, settles down to a normal idle of 600-650 or so. Anybody know what this might be? It doesn't seem normal, as I would expect the tranny to have shifted to 1st a good few seconds before I stop, not as I'm just at a stop, and engine shouldn't still be fighting the stop up around 900-1000 rpm. Trans fluid changed before I got the Jeep a few months ago, only put 2000 miles since I got it, and has been doing it since I got it (hence not sure if its normal). Thoughts please.

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Unread 12-14-2010, 06:05 AM   #2
gdp
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from your description, my GC is the same way, however i don't experience any downshift lunges or issues, my mileage is at 155K. Matter of fact, i don't even really feel a down shift(it dowshifts alot better than a brand new GMC truck i had), but the idle does seem to take a couple of seconds to come down to 650. Mine seems to hang around 800 RPM then come down. But my experience with fuel injected cars (especially automatic transmissions), that this is somewhat normal. So it sounds like your engine is acting normal, but maybe there is an issue with the transmission. I would be alittle concerned about the torque converter fault, if that is not unlocking, it will definitley give you hard downshifts and eventually stalling as you stop.

You may want to clean your IAC valve as a start since it controls idle speed. They tend to get carbon build up.
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Unread 12-14-2010, 09:02 PM   #3
outlaw30
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Thanks gdp. IAC is clean, and it doesn't act like any of the TPS issues I've read on here either...thats why I need some ideas. Guys??

As for the torque converter, it unlocks perfectly, and I never have come close to stalling (high idle is my problem, nothing approaching stalling). The problem is that it doesn't want to lock up in 5th gear. At speeds above 75, it will 'hunt' between 2200 and 2400, also, when accelerating hard at about 60, it seems to slip slightly, ie more revs, not much more acceleration, and my CEL will come on.
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Unread 12-14-2010, 10:12 PM   #4
narnwv
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Quote:
Originally Posted by outlaw30 View Post
The problem is that it doesn't want to lock up in 5th gear. At speeds above 75, it will 'hunt' between 2200 and 2400
this sounds EXACTLY like a TPS problem. If you do replace it only use a MOPAR part.
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Unread 12-14-2010, 10:55 PM   #5
outlaw30
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narn, thanks man. Really? everything i've read on here relates to stalling and such with a TPS. You're saying my lockup issue/hunting rpm at speed (throwing code 740, which is torque convt) is just a tps? I hope you're right, I was thinking my Tq Converter was going bad...
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Unread 12-14-2010, 10:59 PM   #6
narnwv
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Mine "hunted" in that rpm range at high speed and a new MOPAR TPS fixed it. It wasn't throwing any codes at all, but from suggestions here I replaced it and it took care of the issue.
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Unread 12-14-2010, 11:18 PM   #7
DemonButter
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Your TPS could be throwing your RPMs high, low, or out to left field and back. My high rev starts, intermittent near-stall idle (with clean/new IAC), and occasional high speed tranny confusion, all disappeared with nothing more than a new TPS.
Hope your problem is easily solved as well.
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Unread 12-15-2010, 01:25 AM   #8
outlaw30
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thats great news guys, thanks. I hope so too. Have a new TPS ready to go in -- Mopar. For these kinda things, I like OEM.
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Unread 12-25-2010, 11:13 PM   #9
hermitlife
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could you post back whether the tps solved it once you have it installed?
thx
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Unread 01-13-2011, 02:36 AM   #10
tonymartin
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any news on this mate?
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Unread 01-13-2011, 02:52 AM   #11
outlaw30
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Hey buddy. I haven't bothered replacing the TPS yet. Pretty sure its the actual torque converter giving me problems in overdrive. The slight high idle isn't getting any worse, and its not much of a bother.
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Unread 01-13-2011, 03:00 AM   #12
tonymartin
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well we can always throw it on when we do your shocks to test it out if you like? So when will you be wanting to do the shocks anyway? May as well do my injectors whilst we're at it eh? May jump on my fuel pump and rear control arm bushings whilst we're at ie eh? Gonna work us to the bone mate!!! ha ha
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Unread 01-13-2011, 04:09 AM   #13
outlaw30
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works for me, maybe next weekend. I'll call ya.
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Unread 06-08-2011, 02:50 PM   #14
machbuffet
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Hi
Just having a read of your post and I have exactly the same issues re the idle as you come to a stop and the downshift lunge as it shifts into 1st.

Although it may not sound like the usual TPS issues, consider this.

I had idle issues where it would idle at 1100, drop to 650 and do this 3 to 4 times before settling. Same issues with the downshift.
Swapped for another used TPS which appeared to operate fine on another vehicle. Whacky idle issue much better but still the downshift issue.

BOTH TPS tested ok, with both giving .5v at idle and up to 3.8v at wide open, with smooth sweep of the needle in both cases - all as expected.
However, I just decided in the end to buy a new TPS and fit it.
Exactly the same voltage readings but a marked improvement all round in overall.

Idle quality has improved and the 50 RPM bounce has reduced. Smoother idle.
Had also had occasional mild clunk type sensation when slowly accelerating and changing from 2nd to 3rd - that hasn't happened since.
Most noticable though, as I brake and come to a stop, the revs are quicker to reduce to 650 and although I can hear it downshift to 1st, the lunge is all but un-noticable.
I'm crossing my fingers, arms, legs and throwing salt over my shoulder - hopefully it's not a coincidence!!!!
Way I figure it is, for the price of 1/2 hours labour at a shop, you buy a TPS and see how it is - at least you can rule it out.

By the way, I followed the advice on the forum and disconnected the battery. The PCM needs to re-learn the TPS voltage values, otherwise it thinks it still has the same TPS and wil treat the new one like it did the old defective one, with some potentialy whacky results. I left mine for over an hour, while I did some other stuff.
Give it a try - so many of the Trans functions are linked to the TPS that it really should be eliminated early on in ant tranny problems.

Let us know how you get on

Barry
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