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Sticky throttle plates or cable linkage on 2.8L, not closing all the way by itself by hdryder
Started on: 12-07-2013 03:27 PM
Replies: 8 (256 views)
Last post by: hdryder on 12-18-2013 07:54 AM
hdryder
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Report this Post12-07-2013 03:27 PM Click Here to See the Profile for hdryderClick Here to Email hdryderSend a Private Message to hdryderEdit/Delete MessageReply w/QuoteDirect Link to This Post
I just got a '88 2.8L motor running after it had been sitting for a while. I bought the vehicle when it was not running, so not sure how long it was in that condition.
It is running, but has a high idle, and I thought it had a vacuum leak.
Now I realize the throttle is not seating completely closed, and can be closed further when turned and closed by hand.
I had to wrap up the days work by the time I realized this, so I have not spent much time on a trouble shoot.
Does this sound like the throttle body plate area just needs a good cleaning, or could there be other causes for it not to seat closed fully?

The Topic title may not be very accurate, as it really is an issue where the throttle is not completely closing by itself, but can be closed when turned by hand.

Thanks for the help.

[This message has been edited by hdryder (edited 12-15-2013).]

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Raydar
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Report this Post12-07-2013 03:44 PM Click Here to See the Profile for RaydarClick Here to Email RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
It could just need cleaning, or the hole where the shaft goes through could be worn.
I have never seen a Fiero throttle body bind up like you are describing, but I had a two barrel TBI on a 305 to do just what you are describing.
I had a co-worker describe the same thing on a TBI 350.
To fix my 305, I ended up loosening the screws on the throttle plate, and allowing the plate to "re-center" in the bore.
If you do that (does the Fiero TB have screws?) be careful not to break the screws. Maybe use some loctite on them.
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hiwil88formula
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Report this Post12-07-2013 05:22 PM Click Here to See the Profile for hiwil88formulaClick Here to Email hiwil88formulaSend a Private Message to hiwil88formulaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Someone might have messed with the idle stop screw trying to fix a problem before you got it. Check that, I believe there is a way to reset it.
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FieroNate
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Report this Post12-07-2013 05:33 PM Click Here to See the Profile for FieroNateClick Here to visit FieroNate's HomePageClick Here to Email FieroNateSend a Private Message to FieroNateEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm having the exact same problem with my 88 gt. I thought it was a sticky throttle body, but I unhooked the throttle linkage and cruise cable and manually revved it. No problem. Turns out a fray in my cable is causing it to bind. Try unhooking the throttle cable.

There's a chance it's an idle screw, sticky/gunked up idle air stepper motor or a corroded throttle shaft. Could also be a misadjusted throttle plate.

It's rare to have a throttle plate stick but can happen if corrosion builds up on the housing or shaft from sitting. I've seen it on a 305/350 TPI but not on a Fiero.

Might try some Marine Formula 6-56 if it ends up being stuck. It works well on steel to aluminum interfaces.

[This message has been edited by FieroNate (edited 12-07-2013).]

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katatak
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Report this Post12-07-2013 09:19 PM Click Here to See the Profile for katatakSend a Private Message to katatakEdit/Delete MessageReply w/QuoteDirect Link to This Post
There is no "idle screw" on a 2.8 TB. There is a throttle stop screw - if it is out of adjustment - it will not cause the throttle plate to "stick" - it simply limits the travel of the plate. I have had several Fieros that developed a "worn" spot at the accelerator pedal that created a "high idle" issue - Start the car and while it's idling high, reach down and pull up on the gas pedal - if it's worn, you will feel the "catch" and then the idle will drop. Could also be carbon build up on the back of the throttle plate - a good cleaning will cure that.
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hdryder
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Report this Post12-08-2013 11:00 AM Click Here to See the Profile for hdryderClick Here to Email hdryderSend a Private Message to hdryderEdit/Delete MessageReply w/QuoteDirect Link to This Post
Could an incorrect adjustment of the Throttle Valve (TV) cable cause the throttle from closing completely?
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hdryder
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Report this Post12-15-2013 02:50 PM Click Here to See the Profile for hdryderClick Here to Email hdryderSend a Private Message to hdryderEdit/Delete MessageReply w/QuoteDirect Link to This Post
I disconnected the throttle cable, and with it disconnect, the throttle closes completely. So that is what was holding it open a little bit.

Now I need to determine what is pulling a little bit on the throttle cable. I am wondering if the cable bracket at the throttle body end, that is bolted to the upper plenum, is bent back toward the passenger side a little bit too much. I have some of these as spares, that I will look at.

Otherwise, not sure what else could be pulling on the cable. I will look at the suggested pedal also, as a possible issue.

Thanks for the help.
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Fiero84Freak
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Report this Post12-16-2013 01:51 PM Click Here to See the Profile for Fiero84FreakClick Here to Email Fiero84FreakSend a Private Message to Fiero84FreakEdit/Delete MessageReply w/QuoteDirect Link to This Post
I would think you're probably looking at a worn out cable. FieroNate above is probably on the right track. The throttle cable often frays in ways that do not appear to be visual. I had a throttle issue a while back where the throttle flap would not close on my GT, and what was occurring was the cable itself was fraying to where it would "stop" itself when it hit the opening of the actual cable shroud. It didn't look frayed at all, but after I removed the cable I could loosen all tension on it and see it was clearly worn out.

Thankfully throttle cables are super cheap. The Fiero Store has one for $40 that is near OEM reproduction and also has an updated heat shroud - it's actually one of the better products The Fiero Store sells.
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hdryder
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Report this Post12-18-2013 07:54 AM Click Here to See the Profile for hdryderClick Here to Email hdryderSend a Private Message to hdryderEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Fiero84Freak:

It didn't look frayed at all, but after I removed the cable I could loosen all tension on it and see it was clearly worn out.

.


Thanks for the info.
I will inspect the cable over the weekend. I also have a spare cable from my parts car, that was working fine before I dismantled the car.
Does the fraying occur on the throttle body end of the cable, under the cable casing?
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