EFI Throttle Sticks only with engine running.

[Bill Van Vlack]

I have a GM throttle body EFI (EBL) system, and after six years or so, the throttle sticks when lifting the pedal to coast at idle. I can bounce it to make it return all the way. 

I can't make it stick when the engine's off, either by pushing the pedal and slowly releasing, or pulling and releasing the cable at the throttle body.

The throttle body barrells and plates look clean, and I can't feel any movement of the throttle shaft either radially or axially.

Baffled here.....

[bc...@juno.com]

I have seen this sort of problem with high mileage carbs, the so called
shaft bearing (hole in the soft material) gets worn egg shaped and the
throttle plates may scrape. For me it kept changing the idle speed.

The usual fix is to bore for better bearings. Can go badly if they are
badly positioned.
good luck,
Bruce Roe
++++++++++++++++++++++++++++++++++++++++++++++++++++++
[GMCMH-EFI] EFI Throttle Sticks only with engine running.
From: Bill Van Vlack <bill.va...@gmail.com>
To:GMCMH EFI <gmcm...@googlegroups.com>

[Jon Roche]

I would say you need to start by cleaning/lubing the cable.  

Throttle cable connections are very sensitive.   There has been lots of struggles with this at new installs.   Too much return spring and throttle is too stiff.   Also angles it pulls from makes a difference.  

So there is a slim margin of what works, and if not lubed properly it can cause issues.  

On Sep 23, 2024, at 1:53 PM, Bill Van Vlack <bill.va...@gmail.com> wrote:



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[Bruce Hislop]

If the plates are closing too far, they could be binding under vacuum load.   If your IAC counts are on the high side, you could use the idle screw to open the throttle plates a bit more where they might not bind. Your IAC counts could be as low as 5 or so and still have the idle speed under ECM control.

Bruce Hislop

On Mon, Sep 23, 2024, 3:35 PM Bill Van Vlack <bill.va...@gmail.com> wrote:

The plates rest against the throttle stop with the engine off, no matter how softly I release the pedal, or cable at the TB. Turn the engine on and do the same thing and they stick. Maybe vacuum is pulling the plates down and making them bind.

On Mon, Sep 23, 2024 at 12:24 PM BruceHislop <bhis...@gmail.com> wrote:

What is your IAC counts at warm idle.  If you have say 15+ counts at warm idle, you could open the throttle plates a bit more until the IAC counts drops to about 5 or so.  This may  hold the throttle plates far enough off the bore that they don't stick.

Bruce Hislop

[James Hupy]

I always set the idle plates with a .007" feeler gage with the idle stop screw. They will never stick at that setting, and the IAC can easily adjust idle speed.

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[Bill Van Vlack]

Pretty sure you nailed it, Bruce and Jim....

My IAC was at 80 during cold/medium temp idle. I nudged the throttle screw in a little and the IAC came down to 70's and a quick test showed no sticking. So the plates were jammed against the bore. Although when I bounced the throttle earlier the RPMs came down.

At what should the engine temp at idle be when I start should I start adjusting the throttle screw for lower IAC steps?

Bill

[Larry Davick]

I remember a conversation about this some years ago that pointed to the accelerator peddle - bending the upper shaft was the fix. I have the same issue and bought a new throttle cable from Allied but have not driven the coach in too many years.

It wasn’t intuitive to me but it costs nothing to try.

Larry Davick
A Mystery Machine
1976 Palm Beach
Fremont ca

[BruceHislop]

The engine should be at normal operating temperature, so after it has been driven for 15 minutes or so.

BobR stated he likes to see the throttle plates opened as far as possible but with the idle still under IAC control. That way more air gets by the throttle plates carrying fuel., (air going through the IAC carries no fuel). The lower the IAC counts, the more open the throttle plates are, so BobR said an IAC count of 5-10 was good.

You may find, like I do, that the IAC counts at idle are not very consistent.  I'm guessing that my throttle shaft is worn and therefore is not consistent on the amount of air getting past at idle.  My IAC varies from 3-4 up to 10-12 for the same hot idle.

Check your Throttle Position Sensor reading on the DIAG screen of the WUD.  It should show a voltage of about 0.5-0.7 volts with the throttle closed.  Unlike the OEM GM ECM which seemed to be picky about this reading, the EBL just reads the TPS at power ON and if its under about 1 volt, it assumes the TB is at idle setting and saves that voltage reading for idle position for the balance of the power ON until you shut OFF the engine.

Bruce Hislop

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[gbec...@graestone.org]

I have found the same thing. I came to believe that having the plates too far closed caused droplets to “pile up” and then get suddenly sucked down, causing idle variations. This was easy to watch with a light on the plates.

On Sep 24, 2024, at 5:56 AM, BruceHislop <bhis...@gmail.com> wrote:

BobR stated he likes to see the throttle plates opened as far as possible but with the idle still under IAC control. That way more air gets by the throttle plates carrying fuel., (air going through the IAC carries no fuel). The lower the IAC counts, the more open the throttle plates are, so BobR said an IAC count of 5-10 was good.

---------

Best Wishes,

George
gbec...@graestone.org

[James Hupy]

IAC of 5-10 is pretty much right on. To achive this, the throttle plates need to be open from .007 - .010". Do this with a ribbon feeler gage. I have done 7 or 8 Howell EBL systems this way and it is a "set it and forget it" procedure. Also, be really sure you have the correct base gasket under the throttle body. Any vacuum leaks here will make any tuning efforts futile. (don't ask me how I learned this)😩

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