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Unread 11-09-2013, 11:54 AM   #16
derbartman
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ok - I completely removed the throttle body and cleaned it out pretty good. The main part was clean from before, but the side inlet areas were quite dirty - along with the solinoid type thing. I replaced the o-ring for the throttle body ($4) and the oring on the solenoid thing.
What was really interesting to me was the air line which comes in the side of the throttle body from a long plastic hose - had a crack in the rubber hose segment connecting the plastic hose to the throttle body.

got it all back together and checked that it ran - but left testing cold idle until this morning.

unfortunately it wasn't really cold this morning, so it certainly didn't die at a stop, but it did still have the odd rpm drop - so it looks like this throttle body work didn't 'fix' the issue

The behavior is that I come to a complete stop - at first idle is ok, and then perhaps 1 second later the rmp droops significantly - enough to kill it when cold, or just droop to say 400 or 450 with warmer outside temp. and then it recovers after maybe 1-2 seconds. Perhaps Ill try to time it tomorrow morning.

What could this delayed idle speed drop be caused by?

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Unread 11-14-2013, 12:00 PM   #17
derbartman
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Any other suggestions? Do I need to replace the IAC even though it measures ok?
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Unread 11-14-2013, 01:33 PM   #18
Jeeples
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Check voltage for the TPS (Throttle Position Sensor) throughout it's operating range. It's easy enough to check with a volt meter, there's several how-to's on youtube. It's possible that the TPS is reading high, causing the IAC to close all the way, since the ECM thinks the throttle blade is open more than it really is.
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Unread 11-14-2013, 02:09 PM   #19
BustedZJ
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Quote:
Originally Posted by derbartman View Post
What was really interesting to me was the air line which comes in the side of the throttle body from a long plastic hose - had a crack in the rubber hose segment connecting the plastic hose to the throttle body.
a vacuum leak that close to intake would be a good place to look. check all vacuum hoses. they will cause poor idle, especially when you first release the gas, and can cause poor mpg, which i am sure is already bad in a v8...

either replace that cracked piece of hose or try to seal it with some silicone or similar. check the other vacuum hoses.

can check for leaks with some carb cleaner spray. spray it over the cracked area and any other possible leaky hoses, if the idle speed changes you have found a leak.

i wouldnt throw parts at it especially if you tested them and they came back fine, that can get expensive.
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Unread 11-16-2013, 10:44 PM   #20
derbartman
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ya - I did replace that segment of hose - with no noticeable improvement. I need to research how to do this measurement on the voltage or resistance of the TPS - and I guess next checking vacuum hoses seems plausible.
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Unread 11-17-2013, 04:40 PM   #21
86cj74.2L
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With a scanner that reads live data its easy. Just watch the TPS.

Idle is around 11.3% and full throttle is around 78% or so.

It should be steady when your holding the throttle steady and as you slowly increase the throttle the number should increase accordingly.

On my Saturn my old TPS would actually go down at a few points where I mostly drove at. Say......around 11-15% and in the mid 20's.
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Unread 11-17-2013, 05:01 PM   #22
99_wj_QD
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Don't even mess with cleaning that dam IAC, just go out and buy a new one, I can %100 guarantee you that is your cause of this issue, simply because driving with two feet to maintain a slightly open throttle plate makes the issue go away...

New IAC, clean up that throttle body nice and purdy when you are replacing the old IAC, and also make sure you wind that pintle on your new IAC all the way down into the motor housing prior to installation.

I would buy a Mopar IAC, when mine went bad I bought one from o'Reilly and it ended up coming apart inside my throttle body one day causing a no start...had to fish out the internals from the tb and put the entire IAC assembly back together...when it comes to anything electronic always go OEM
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Unread 11-19-2013, 12:21 PM   #23
derbartman
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ok - I didn't know about winding the pintle (don't even really know what that is) maybe I left my current one all wrong when I had it out cleaning.

I watched a youtube showing measuring the voltage on the TPS, but to measure while its plugged in I think I need a very thin probe - I don't want to mess up the gasketing on that connector - I did measure the resistance of the TPS without voltage/power and it seems ok.

Ill try this OBD approach looking for steady - the fact that its only at cold though might make this whole measuring approach a bit hard.
I like your confidence QD - and I have to say im not convinced of TPS - I may just spring for that part instead of more messing around - I bet its $90 or so though..
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Unread 11-19-2013, 01:22 PM   #24
86cj74.2L
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Of its only happening during warm up watch the open loop / closed loop on your scanner and see if it acts up while still in open loop or if it happens right after it goes to closed loop while warming up.

Also look at your LTFT's.
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Unread 11-19-2013, 02:22 PM   #25
derbartman
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LTFT is?

I hope I can see open loop / closed loop on my scanner - this is part of the warm up cycle?
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Unread 11-19-2013, 03:52 PM   #26
86cj74.2L
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Quote:
Originally Posted by derbartman
LTFT is? I hope I can see open loop / closed loop on my scanner - this is part of the warm up cycle?
If your LTFT's are high like approaching 10 or higher it could represent a fuel delivery problem, or a vacuum leak (big).
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Unread 01-15-2014, 12:33 PM   #27
derbartman
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I was able to get my LT ST - but I didn't write down the numbers - Ill need to go back and do that.

I have discovered that if I put the jeep in neutral when stopping I don't have this issue. I once found a thread in this forum where someone had a symptom just like mine and they claimed both the p1784 and this type of dying was solved when they opened up the tranny and fixed some kind of leaking gasket I think. I do sometimes get this P1784 - on cold cold mornings and get this high slipping mode - but I always perceived that and this idle issue as separate, but now I think they are linked or the same..
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Unread 01-16-2014, 04:59 AM   #28
86cj74.2L
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It is very worth looking into solving the P code. But it looks like many things can cause it. From bad wiring, bad sensor, bad pump, bad VB.........
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Unread 01-17-2014, 05:55 AM   #29
Double E
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I have the same thing happen to me when the battery is weak. When the engine returns to near idle, the old alternator can't keep up with the need and relies on the battery to supplement. The weak battery causes a power drop and idle fluctuation. As it got colder and the battery older, it would stall at a light unless I did a gas/brake combo. Then a Neutral drop to leave from a light.

That occurred exactly twice before I had enough of that and got a new battery. All was good then I had the alternator finally fail a few years later.

(At least let a parts store clerk do a load test on the battery to rule that out, right?) Just reading voltage won't tell you enough.
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Unread 01-17-2014, 08:55 AM   #30
ZJPunk98
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Quote:
Originally Posted by rdkendrick View Post
I have a 2002 FSM that I bought when I had a 2002 Overland. When that got totaled, this FSM pretty much still applies to my 2003 Overland. Thanks for the offer, but I was saying that mostly for the benefit of whoever is reading the post. I searched and search, but could never find the free versions either. People on here keep saying there are free FSM's out there, but never give a link, and I could never find them.

Sent from my iPad using my fingers
www.jeepslimited.com

create an account and you have access to FSM downloads for all makes and models. This site relies on donations to run, so feel free to donate.

They are also looking for the 02' FSM, you could donate a copy of yours to their inventory. In fact, I would download a copy of it.

I currently cross reference the 01' and 04' manual when working on my jeep.

Help them out, as they help lots of jeepers nation wide.
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