2004 TJ 4.0 High Idle after Drive, but then normal idle - JeepForum.com
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post #1 of 7 Old 03-31-2011, 09:01 AM Thread Starter
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2004 TJ 4.0 High Idle after Drive, but then normal idle

I have an issue I have been challenged with for some time & have replaced a lot of parts & searched many forums - found similar issues, but none where the idle returns to normal. Any input is appreciated.

2004, 4.0, 5 speed, 4.5" rubicon super flex, 4.56 gears, 31" tires, Airaid intake, 62mm throttle body, banks header, no muffler (only the 3 cats), only 79,000 miles (see also - www.DuneToyz.com )

Here's the deal -
- start the Jeep in the morning & drive it in town - just fine.
- but at any time, if I get on the freeway for a period of time driving at a set speed, lets say 65, when I stop, my idle is high - 1200rpm - if I get in stop and go traffic, this can be a bit annoying
- but if I get stopped for long enough or at a stop light, the computer auto-corrects & brings the idle back down to normal.

Here is what has been replaced in the last 6 months
- catalytic converters are all new
- I tried another 62mm throttle body
- new TPS and IAC
- new intake/exhaust manifod gasket
- both pre and post o2 sensors
- have not found any vacuum leaks & return to normal idle wouldnt appear typical of a vacuum leak
- I even replaced the crank sensor the other day

The last thing I can think of that I have had issues with before, but it always exhibited power problems, is the fuel pump - I have actually already gone through 3 or 4 fuel pumps in this beast (but while it looks like a baby and I take extremely good care of it, I do run high RPM and use the rev limiter when thrashing around in the dunes) - or maybe a leaking injector?

But in this year Jeep - there is no schrader valve on the fuel rail.... so I am going to have to fab up a loop with a tee with a valve in it - so I can connect an electronic sending unit - I have fuel pressure gague kit so I can monitor real time - just need to get it hooked up.

I have a decent Actron scan tool that can record and chart and stuff - but there doesnt seem anything odd - TPS is at normal position - even when idle is high, of course the MAP changes because of the idle speed, but at normal idle it seems fine, intake temp sensor seems to be reading correctly. o2 sensors seem to have normal readings.

Any suggestions for this phenomenon will be appreciated.

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post #2 of 7 Old 03-31-2011, 09:30 AM
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I would look at the IAC again. When it us doing it disconnect the connector and see what happens. If it corrects or isles down there is your problem.
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post #3 of 7 Old 04-05-2011, 06:03 PM Thread Starter
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here is an update.....

I removed the replacement IAC & TPS I had purchased from AutoZone and compared them to the OEM parts.

- Autozone - 6.7% at idle and 71% at WOT
- OEM - 11% at idle and 79% at WOT

but probably the biggest variation was in the IAC
- Autozne IAC - cone at the end of the shaft was longer and wider than the OEM part

When I removed the Autozone IAC - it was retracted almost half way, even though the jeep had just been idling - interesting

I had replaced the TPS originally because it had been sticking, I cleaned it and tested and no more sticking

Re-installed the OEM TPS and IAC (disconnected battery to reset computer) - guess what? - back to 100% good - idle is just fine when comming down from freeway or cruising in town. No more issues.
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post #4 of 7 Old 11-05-2012, 08:41 PM
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I have the same problem, but the IAC and TPS didn't fix mine. Any other ideas?
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post #5 of 7 Old 11-06-2012, 11:52 AM
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Originally Posted by seabass2020 View Post
I have the same problem, but the IAC and TPS didn't fix mine. Any other ideas?
I had this problem...it seems to me that when I cleaned the throttle body a few months ago, that the cleaner may have dried out the bearings in the butterfly (I was unfamiliar at the time with tearing it down completely).

I got my idle to stick, pulled over, took off the tube and found that the butterfly was sticking ever so slightly.

I took it completely apart, cleaned and regreased the bearings in there, and have had no trouble since.
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post #6 of 7 Old 11-06-2012, 03:28 PM
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I have cleaned the tb and its definitely not sticking
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post #7 of 7 Old 11-07-2012, 12:52 PM
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My only suggestion to the issues, never use auto store sensors. I had the same things at first, replaced it with a autozone TPS. Problems went away then came back, when I went to check the plug on the TPS, the damn thing fell apart in my hands. Got one from the dealership, but it fixed my issues right away. I know the dealership parts are more expensive, but they are cheaper then replacing the same part twice.

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