I've noticed that when the throttle is closed it doesn't rest against the idle stop. The thing that holds it closed is the butterfly valve itself against the throttle body neck...
Is this okay or can the throttle valve "wear down" the body intake? I also can't seem to find the idle stop screw - there's nothing there. There is a little cap/groove where I "guess" the screw head should be but nothing that seems removable.
v6 or 4 cylinder? i had a similar occurrence when building an engine for my low mileage 84, a little history, car had 60,000 miles when i got it, but engine was bad, rod bearing, windowed block, anyways, built a nice 4 cylinder for it and had an original 84 throttle body i used on it. couldnt get rid of check engine light, was giving all kinds of codes, egr, tps, iac, changed all of that and didnt help. by accident i was messing with the linkage and found excessive play in the throttle shaft, not allowing it to close properly and probably sucking air around it as well. i found a nice low mileage throttle body and made sure the shaft was good, put it on and all problems dissapeared
I'm not an expert in throttle body but do not touch this screw. It had been seted up by the manifacture. I did that mistake and i had to pay big money to reset it and make sur my idle was running fine. If you touch it the rpm goes high and high till you stop the engine and let it cooled down. Mine start at 1000 1/4 mile away was at 2500 and another 1/4 mile away was at 3500 and finaly reach 5000. I was suspecting vacum leak but was that screw.
Sorry, forgot about the engine. It's an '85 duke automatic.
I had the TBI rebuilt and have no idea if it was that way to begin with. There was no play in the shaft and I always remembered the throttle was a little "sticky" when revving up the engine by hand at the throttle linkage (before the rebuild) so I guess it could have been always this way.
The question remains - should I mess with it to get the throttle plate stop against the idle stop or can I drive it as it is?
The car runs fine, no codes, etc.
[This message has been edited by cebix (edited 07-04-2015).]
Yeah but I'm worrying if the throttle plate wears out on me it's gonna be a huge pain to fix it... So I'm asking if it's a good idea to bring up the idle stop to the point where it rests now. If yes how do you adjust it since there is no screw there:
I guess that's where you should be able to adjust it?
It looks like the screw hasn't been adjusted because to get to the screw the plug over it has to be drilled out. You have another problem and messing with that screw most likely won't help. Maybe the throttle cable is binding. How high is the idle?
Idle is fine, everything runs fine. It's just that when the throttle plate is closed it doesn't rest on the idle stop, there is a 2mm gap.
I couldn't get a good pic, but here it is, you can barely see it - the throttle "lever" when closed doesn't rest against the idle stop. The force that holds it in the closed position is the throttle butterfly plate against the inner wall of the throttle body.
[This message has been edited by cebix (edited 07-04-2015).]
I've noticed that when the throttle is closed it doesn't rest against the idle stop. The thing that holds it closed is the butterfly valve itself against the throttle body neck...
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Originally posted by cebix:
I had the TBI rebuilt...
Something is wrong. The butterfly should not be binding in the throat of the TB.
If it was my TB, and the idle stop screw was not making any contact, I'd do whatever it takes to correct that. However, only adjust the idle stop screw if you've ruled out every other possible reason for the binding. Any chance the butterfly valve was removed during the TB rebuild and it wasn't reinstalled correctly?
[This message has been edited by Patrick (edited 07-04-2015).]
(...)Any chance the butterfly valve was removed during the TB rebuild and it wasn't reinstalled correctly?
Yeah it was removed. Can't see how it could be reinstalled incorrectly. My guess is it was like this before - either the "outside lever" that should touch the idle stop is bent or... I don't really know. So to adjust the screw you need to drill out a hole? I guess I'll just add something on the "lever" so it makes contact with the stop when fully closed then.
EDIT: Couldn't find a Fiero one but you get the idea what I think is for some reason bent:
EDIT2: You can see (kind of) on my previous picture that the little tab is not exactly at a 90 degrees angle relative to the shaft - it's a little off. Is that normal? I don't see what force could have bent that. If it was at perfect 90 degrees it should make contact with the idle stop.
[This message has been edited by cebix (edited 07-04-2015).]
How is that possible? The shaft has an area which is cut out for the butterfly and the butterfly is flat. The butterfly can only go in two ways (rotated 180 degress or upside down but it's still flat). Nothing is adjustable on the shaft. Can you specify what can go wrong there? It's going to be a pain tearing the whole TB down again if you're suggestion is correct.
As I mentionted I always felt it was "sticking" to get off the stop position even before the rebuild (can't feel it by pedal, but is obvious when done by hand on the shaft itself) - but didn't notice if it wasn't reaching the stop before. Don't know what previous owner (or owners) might have done there.
[This message has been edited by cebix (edited 07-04-2015).]
I haven't had a Fiero 4-banger TB apart, but on carbs I've disassembled, the sides of the butterfly valve are beveled. The butterfly valve therefore needs to be reattached to the shaft in a certain orientation.
I have no idea what your TB was like before or after its rebuild... but the idle stop screw not making contact with anything indicates to me that something is wrong somewhere.
Idle stops are seal from factory but Sadly Idle stop can vibrate loose over time or other problems that need to adjust the stop. When that happens you need to pierce and remove cap w/ ice pick, etc.
Correct method for adjusting/resetting each type are in my cave, Idle Stop
If screw is loose in the threads, try rapping w/ pipe sealer tape. Do Not LocTite etc. IF you need to fix it later, any loctite will be a big problems because aluminum and red, blue, and green formulas are made for big bolts. (Loctite does make a small screw lock but this screw is in aluminum.)
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Don't drill the cap. It's a simple thin metal piece wedged in the hole with the stop screw underneath. As Ogre said just stick a sharp metal tool through the cap and wedge it out.
And just for reference, the stop screw is NOT an 'idle stop screw' as the idle is handled by the Idle Air Control motor via commands from the ECM. The one and ONLY purpose of the screw is to keep the throttle plate from getting stuck in the bore. If you had the proper ECM monitoring equipment you can set the stop screw so that the IAC motor is commanding 25-30 steps for a nice smooth idle. The range is 1-50 steps. What happens is folks try to fix a low idle by adjusting the stop screw. This only messes up the ECM as it is trying to set idle through the IAC motor.
If the butterfly is hitting the inside bore of the throttle body it generally will want to stick. It will be irritating when you press on the gas pedal and it takes some effort to get it unstuck every time you press on the gas pedal. So adjust the screw to move it from hitting the inside of the TB bore and the IAC valve will self adjust to make the idle correct. I had this in a Saturn once. Every several months I had to turn that screw in because it kept backing out and started sticking.
------------------ Rodney Dickman
Fiero Parts And Acc's Web Page: All new web page!:www.rodneydickman.com Rodney Dickman's Fiero accessories 7604 Treeview Drive Caledonia, WI 53108 Phone/Fax (262) 835-9575
@Patrick: The throttle plate is not beveled, there's no way I see it could be installed wrong.
I'm not saying it is installed wrong, but was just making the suggestion that it might be possible (since you stated that it had been removed). If you've double-checked it, and it's fine... great. Basically the point I was making was to not assume that it's okay.
Originally posted by Hudini: And just for reference, the stop screw is NOT an 'idle stop screw' as the idle is handled by the Idle Air Control motor via commands from the ECM. The one and ONLY purpose of the screw is to keep the throttle plate from getting stuck in the bore. If you had the proper ECM monitoring equipment you can set the stop screw so that the IAC motor is commanding 25-30 steps for a nice smooth idle. The range is 1-50 steps. What happens is folks try to fix a low idle by adjusting the stop screw. This only messes up the ECM as it is trying to set idle through the IAC motor.
GM Service Manuals call this screw as Idle Stop or Throttle Stop depending actual book/section and My cave page have correct adjustments from FSM for both TBI. (I'm rereading V6 section and I think base is a bit too high at 800RPM but having a hard time to find right base #. I'll check 87-88 books too later.)
Screw sets Base Idle and IAC sets idle used after. This screw guaranties minimum idle to start the engine. Just like you set Base Timing of Distributor engines then ECM Timing can advance or retard timing as needed. ICM is very dumb and uses Base Timing to start the engine. ECM won't take over Until engine is over ~400 RPM.
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Originally posted by Patrick: They can be installed incorrectly. I just find it difficult to believe that this is the way the TB was set up at the factory.
Most times yes because the butterfly edge are "beveled" a tiny bit so it can competently close the bore. This is done in most TB TBI and Carburetors. I don't have a 300 TBI to see if this it true. I have rebuilt 700 TBI (87 duke) and is true for them.
If installed wrong or not... you often can see this just looking down the bore and stop screw to allow throttle to close.
