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Hanging idle

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  #1  
Old 01-29-2017, 06:58 PM
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Default Hanging idle

1997 ram 1500, 4x4, 408, NV 4500.

As the title says, I'm having issues with hanging idle. This started a few months ago intermittently. To begin with, it would only show when logging a tune for Ryan, and only on occasion. As we progressed with the tune it became more consistent... Only while running his tune.
Starting around the end of November it started doing it even with the original tune I started with (Hemifever canned 91 octane tune), and the factory tune.

Once I realized it wasn't a glitch in the tune causing it I started looking for vacuum leaks, or anything I could think of that might cause it. New IAC (MOPAR)-no change, new TPS (MOPAR)-no change, cap all vacuum lines (except MAP)-no change, and of course go over the intake thoroughly.

The only good(?) thing is how consistent it is. Whether coming down from driving, or blipping the throttle from idle. It will hang at 1700 rpms for 1 or 2 seconds, then 1200 rpms for 7 to 10 seconds. Then it will fall smoothly to where it's supposed to be (750). The only vacuum stuff running on this truck is climate control and brake booster. The previous motor had vacuum issues, so I eliminated everything else.

Anyone want to bounce some ideas my way on this? I'm at a loss. It has done the same with 3 IAC's (good functioning from previous motor, new Napa, new MOPAR) 3 TPS's (same as IAC), and 3 MAP's (same also).

Thanks for reading my novelette.
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Old 01-29-2017, 09:49 PM
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Well that's odd...... Is the pintle hanging in the bore?

Think I would trace the wiring, and check the connectors at the PCM, and IAC.
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Old 01-30-2017, 12:20 AM
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I'm leaning more towards something like a throttle cable binding somewhere.
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Old 01-30-2017, 07:18 PM
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Stock throttle body? Put a scanner on it and see what the tps is reading.
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Old 01-31-2017, 01:42 AM
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Quote:
Originally Posted by HeyYou View Post
Well that's odd...... Is the pintle hanging in the bore?

Think I would trace the wiring, and check the connectors at the PCM, and IAC.
I didn't think of the pintle hanging up. Is there an easy way to check it?
Hopefully you're not onto something with the wiring. I really don't feel like tearing that loom open again.

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Originally Posted by dbbd1 View Post
I'm leaning more towards something like a throttle cable binding somewhere.
Cable and butterflies are moving smoothly. Have checked them a few times.

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Originally Posted by Moparite View Post
Stock throttle body? Put a scanner on it and see what the tps is reading.
Bored out stocker from HiPoTec, 52 mm. It's been a little bit since I looked at the TPS readings, but IIRC they were 9%-89% on all three. Testing with an analog meter showed a smooth sweep with all 3 also.


Thanks for the good ideas so far. Please keep them coming. I'll look things over again this weekend when I should finally have a few minutes.
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Old 01-31-2017, 07:57 AM
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If you had a fairly high-zoot scanner, it gives the opportunity to manually control IAC..... I *think* the snap-on mt-2500 will do it..... the newer (more expensive) ones certainly will.
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Old 01-31-2017, 10:56 AM
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Does it hang with only your foot off of the throttle or also if tap the brake?
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Old 01-31-2017, 05:37 PM
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The manual computers hang at about a 1000 RPM until you come to a complete stop. Not sure if this is similiar to what youre describing.

If im coming to a stop and put the clutch in it hangs at about 1000 or a little more RPM until i come to a complete stop. Its a function of the computer for the manuals.
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Old 01-31-2017, 10:29 PM
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Quote:
Originally Posted by dbbd1 View Post
Does it hang with only your foot off of the throttle or also if tap the brake?
It hangs under all normal circumstances. Don't ask what abnormal circumstances might be, I haven't figured it out yet lol. No variance that I've seen with brakes. Curious where you're heading with this thought though.

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Originally Posted by Ham Bone View Post
The manual computers hang at about a 1000 RPM until you come to a complete stop. Not sure if this is similiar to what youre describing.

If im coming to a stop and put the clutch in it hangs at about 1000 or a little more RPM until i come to a complete stop. Its a function of the computer for the manuals.
Since this is an auto trans computer with a trans delete flash, I'm not sure if it would apply. That being said, it does it whether I'm moving or not....
That makes me curious now though because I bypassed the neutral safety. Depending on how Hemifever does his trans delete stuff, the truck might think the clutch is in all the time...
Of course, that doesn't explain why it's just recently (relatively speaking) started doing this. I've run with this tune for a few years now. Only change to mention is the 408 instead of the 360.

Sorry about the rambling. Just thinking in print.
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Old 01-31-2017, 10:48 PM
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Quote:
Originally Posted by HeyYou View Post
If you had a fairly high-zoot scanner, it gives the opportunity to manually control IAC..... I *think* the snap-on mt-2500 will do it..... the newer (more expensive) ones certainly will.
I forgot to catch this one earlier. The MT2500 does allow control of the IAC. I played with it quite a bit when I was loaned one from Wildman for setting my fuel sync. The snap-on allows a lot of things to be checked.
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