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04 4.0 idle extremely high

Old 04-12-2019, 08:08 PM
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Default 04 4.0 idle extremely high

Hey guys,
Replaced the IAC, TPS, MAP sensor cleaned the Throttle body, send the computer off to be reset.

Im stumped.
My daughter bought an 04 GC Larado with 150k miles.
Had to feather the gas to get started. Then it was SKIM locked, so I sent the computer off to reset. I replaced the IAC.
It fired up and went straigt to 3k rpm.
So I got another IAC and bam... 3k idle.
Replaced the TPS... 3k idle.

Reset the computer, unhooked battery for a week.
Unplugged MAP sensor. And fired it up. Ran for a few seconds and died. But idle was lower (win).

Noticed a big vacume hose was off. Plugged it back in. And attached MAP plug. That lowered the idle to 1700-1800.
Then tapped the throttle hoping it would lower the idle... bam... back to 3k rpm.
What the hell?

Im just trying to get my kid back on the road. But she aint going anywhere if its a runaway vehicle.

Help me please.

Last edited by ForrestLee; 04-12-2019 at 08:11 PM.
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Old 04-14-2019, 08:13 AM
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You still have a massive vacuum leak somewhere, probably. Put a torque wrench on the header/intake bolts and make sure they are still tight to specs. Fully inspect all the connections on the intake manifold (basically anything downstream of the throttle body) and related systems.

Easiest way to find a vacuum leak is a smoke tester. You can build your own for about 50 dollars worth of parts that you can get at Wal Mart and Lowes. It'll help find even the smallest vacuum leaks.

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Old 04-14-2019, 01:05 PM
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Alrighty. Ill give that a try. I looked pretty well, but didnt try the water or starting fluid tests. Ill make the smoke tester...
Thanks!
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Old 04-17-2019, 12:39 PM
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Check for any codes if you havent already.
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Old 04-17-2019, 07:24 PM
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Originally Posted by fb97xj1 View Post
Check for any codes if you havent already.
Codes are
Stored.
po505, po108 (MAP/Barometric Pressure Circuit high

Pending
Vehicle speed sensor
po500

I did a live test. Map 6.0 idle around 1800... that was new IAC, MAP and TPS.

I replaced the IAC with the original I thought was faulty.
Map 5.7, RPM 1618
VSS 0
Spark 3.0

Also, I grabbed a dent puller suction cup and closed off the intake, it died. So if it has a vac leak, its pretty small.
This thing is a grandma owned jeep. 154,000 miles.
Ive looked at all the vacuum lines, all are attached now. And its not sucking enough to keep it running when I shut its mouth.

Im sure its in the computer. I sent the ECM off to Florida to get the skim lock, unlocked. I also unplugged the skim reader under the steering column, before putting the ECM back in, so I can start it. Because it was a low idle, non start issue... that locked it to begin with. Too many tries.
The only thing I fixed before this happened was the ECM getting the skim turned off, and the IAC that was the problem to begin with.
Is it possible that the ECM had learned the bad IAC information and after I got the ECM back with a new IAC installed, it was still thinking it needed to max the air flow rendering the new IAC useless?

All I know is I'm over $2500 deep into a vehicle my daughter can't use, and I'm out of funds to fix it. (And patience)
All my Middle TN Jeep loving friends, help me figure this out please.
At this point I'm about to sell it. My kid needs a vehicle that will run. She really needs this one to work.

Any other ideas?
Any tuner guys in the Humphreys County TN area that can program an 04 Cherokee?
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Old 04-17-2019, 07:28 PM
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Also
If I move that dent puller till there is a hair opening for the air to get through, it idles smooth at around 500 rpm.
So go figure...
This is a bone stock jeep as far as I know.
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Old 04-17-2019, 08:46 PM
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Closing off the intake while it's running could be causing enough vacuum to pull whatever is leaking closed. Putting a torque wrench on the intake/exhaust manifold bolts and checking them is free. Then again if the combo gasket has failed at some point no amount of tightening it will get it to seal properly.
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Old 04-18-2019, 08:59 AM
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It ran perfectly before the skim was removed. The only difference was the idle was too low.
If it had a vacuum leak, it would have had a high idle prior to the ecm being removed and sent to have the skim removed...

Its not a vacuum leak.

Who around me has an ecm tuner tool.
Im in Waverly TN. I know we have a few Jeep guys around.
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Old Yesterday, 12:01 PM
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Some time back I replaced the TPS on my 97 4.0 L because if you touched it with your fingers and wiggled it while running the idle would vary up and down. I purchased a new TPS from the dealer and installed, same issue if you touched it and wiggled it, the idle would shift up and down but not as much. I purchased another from Auto Zone and installed it, problem gone. The TPS is a resistance device so I spliced the pig tails from the new TPS to the harness with solder connections, I don't trust crimp connectors over the long haul.

BTW when I removed the TPS from AZ packaging, it was in a Chrysler sealed plastic part bag. Same part but much less $$. New parts don't always behave like new parts. Just saying.

Good Luck.
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