3.5L High Idle

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3.5L High Idle

Postby RainbowSprinkles » Tue Jan 10, 2017 2:41 am

I have read many of the other high idle threads. Still have a high idle, UGH.

I have tried posting elsewhere with little luck and have done the searches and tried the suggestions.

I replaced the (IDC) idle control valve. I have replaced the EGR and cleaned all tubes. I have run sea foam through the intake until no more smoke. I have replace the spark plugs. I have replaced the bad 02 sensor.

The only check engine I have now is on and off at times, its the Cat code so I doubt related.

When I reset the ecu the idle relearns temporarily and sounds good, but then after 3 or so restarts its back to 1700rpm-2000rpm ish and constant. It will stay there until I put load on it. So if I put it in drive its 1100 and sounds good. Reverse, 1100. Any time I take load off, Park or Neutral its back to 1750 or so and just idles there.

Any suggestions?
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Re: 3.5L High Idle

Postby chimpboy » Tue Jan 10, 2017 3:48 am

Vacuum leak? This would potentially include a leak via the inlet manifold gasket at the block.
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Re: 3.5L High Idle

Postby RainbowSprinkles » Tue Jan 10, 2017 10:09 am

It has to be. I'll test for it. Thanks.
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Re: 3.5L High Idle

Postby remogw » Wed Jan 11, 2017 12:20 am

Take a look at the fuel pressure regulator (FPR) hoses. I had an erratic rpm low to high and found that the vacuum hose coming from the back of the manifold to the FPR was cracked on both ends. Replaced it and fixed the problem. It is on the fuel rail, left side, all the way in the back.
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Re: 3.5L High Idle

Postby chimpboy » Wed Jan 11, 2017 1:41 am

remogw wrote:Take a look at the fuel pressure regulator (FPR) hoses. I had an erratic rpm low to high and found that the vacuum hose coming from the back of the manifold to the FPR was cracked on both ends. Replaced it and fixed the problem. It is on the fuel rail, left side, all the way in the back.


Good point that is the exact one hose I had to replace when I did my engine swap. It was about to fail at the regulator end.
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Re: 3.5L High Idle

Postby Plimbob » Wed Jan 11, 2017 1:54 pm

I had the same exact issue with our 99 Passport 3.2L and replaced many of the parts you have outlined, including re-establishing a solid ground and disconnecting the pressure sensor on the power steering unit. Also replaced the coolant temp sensor on the manifold. None of this had any consistent effect.

I ended up finding a tech in our community who had worked for a large Isuzu dealer in Dallas and took it to him. He found there was inconsistent voltage at the TPS, it didn't fluctuate enough to set an engine code. He tested over a period of a week at different intervals and determined that was a possible solution along with some connection issues at the computer. He corrected the poor connections and replaced the TPS and its been idling properly since?

There is a shop bulletin out on the web from Honda regarding the various possible solutions to this problem with the 3.2L in the Passport which is the Isuzu engine.

Hope that helps...
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Re: 3.5L High Idle

Postby RainbowSprinkles » Wed Jan 11, 2017 4:50 pm

Interesting thoughts guys. I don't have my truck back yet as my wife has confiscated it temporarily due to her 4runner being repainted at the shop (long story). When I get it back, I'll check all vacuum tubes especially in the area mentioned. However, my idle is not sporadic at all. It is extremely steady and consistently way high. I would guess something near the intake manifold in that case?
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Re: 3.5L High Idle

Postby Ed Mc. » Wed Jan 11, 2017 8:19 pm

Welllllllllllll............it's not an uncommon problem for these to have cracked/leaking intake manifold gaskets!

That would certainly give you a nice vacuum leak.

You might try chasing leaks around the intake manifold area with a spray of WD-40 or Marvel Mystery Oil, etc.

You may find the idle changes when the lube spritz temporarily seals the leak.

No doubt there are quite a few threads here about that problem, if you do a search.

Here's one post I found with good words from Jerry Lemond on the topic:

viewtopic.php?f=1&t=66993&p=579950&hilit=cracked+intake+gasket#p579950

An older post with lots of good info: viewtopic.php?p=7229

HTH.............ed
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Re: 3.5L High Idle

Postby RainbowSprinkles » Sat Jan 14, 2017 2:50 am

Ed Mc. wrote:Welllllllllllll............it's not an uncommon problem for these to have cracked/leaking intake manifold gaskets!

That would certainly give you a nice vacuum leak.


Guess what? You sir were right.

It's not just a small leak, the entire gasket is sticking out in about a half inch area... It's ridiculous.

Tomorrow the entire manifold comes off and the gasket gets replaced. Thanks all for the help.
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Re: 3.5L High Idle

Postby Ed Mc. » Sat Jan 14, 2017 3:04 am

RainbowSprinkles wrote:Guess what? You sir were right.

It's not just a small leak, the entire gasket is sticking out in about a half inch area... It's ridiculous.

Tomorrow the entire manifold comes off and the gasket gets replaced. Thanks all for the help.


Wow! Massive air leak, that would sure do it! Saw lots of comments about poor idling, etc, but we can add that one to the books, I reckon!

OE gaskets or Fel-Pro should do the trick. Get hold of Jerry Lemond for the OE stuff.

You can look up aftermarket gasket sets at rockauto.com:

http://www.rockauto.com/en/catalog/isuz ... asket,5424

Glad it wasn't anything worse, at least this is a fairly inexpensive repair..........ed
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Re: 3.5L High Idle

Postby RainbowSprinkles » Sat Jan 14, 2017 3:08 am

Ed Mc. wrote:
RainbowSprinkles wrote:Guess what? You sir were right.

It's not just a small leak, the entire gasket is sticking out in about a half inch area... It's ridiculous.

Tomorrow the entire manifold comes off and the gasket gets replaced. Thanks all for the help.


Wow! Massive air leak, that would sure do it! Saw lots of comments about poor idling, etc, but we can add that one to the books, I reckon!

OE gaskets or Fel-Pro should do the trick. Get hold of Jerry Lemond for the OE stuff.

You can look up aftermarket gasket sets at rockauto.com:

http://www.rockauto.com/en/catalog/isuz ... asket,5424

Glad it wasn't anything worse, at least this is a fairly inexpensive repair..........ed


Thanks for the help. I like to wrench and find it therapeutic, so I'm in for a couple hours tomorrow of disassembly and reassembly. The to make some fun mods. Thanks again.
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Re: 3.5L High Idle

Postby chimpboy » Sat Jan 14, 2017 5:20 pm

While you're at it have a look inside; there is a good chance that the inlet manifold (and the throttle body for that matter) could use a clean up.
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Re: 3.5L High Idle

Postby RainbowSprinkles » Sat Jan 14, 2017 6:36 pm

Good call. I have a good habit of cleaning things when exposed.
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Re: 3.5L High Idle

Postby RainbowSprinkles » Sun Jan 15, 2017 7:50 pm

New gaskets in place. Problem resolved. Everything cleaned up and reinstalled. Running like a top.

Lots of pictures and details of the work to fix this in my build thread. Direct link for reference http://forum.planetisuzoo.com/viewtopic.php?f=15&t=97754&p=5205313#p5205273
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Re: 3.5L High Idle

Postby ducktrooper1 » Tue Jan 17, 2017 11:55 am

My 99 Trooper has been idling very high for some time but since I only drive it 3 months of the year(hunting season), I haven't really fooled with it. What would you guys estimate the shop labor cost to run for replacing the manifold gasket? I have the part from Jerry....just never got around to doing it. Thanks!
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