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Thread: Throttle Sticking - any ideas for fixing?

  1. #16
    Fuel Injected!
    Join Date
    Mar 2015
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    65
    Thanks all for the responses. Here I'll try and respond to all the comments, and recap a few things.

    I've tested vacuum and it's normal.
    I've checked IAC counts, and when hot and idling it's single digits, around 5.
    It cannot be either cruise or throttle cable, because I was able to get the throttle to stick with both cables detached by manually adjusting the throttle.
    I've remove the TPS and done the same, so the TPS is not adding any binding force.

    It ONLY sticks when the engine is running.

    Previously I thought I stripped two of the torx screws. It turns out I twisted and cracked the splines on my craftsman driver, so I ordered high quality Wiha driver from mcmastercarr, and it worked great to remove the screws.

    When it's running, and the throttle is sticking, when I remove the map sensor vacuum line, allowing a direct port to atmosphere, the throttle returns to the close position immediately. The force from the vacuum / air flow past the blades is contributing to the sticking.

    I am disappointed in two aspects of the throttle shaft. First, there is more play than I'd like, consider it has newly pressed in brass bushings (noticed in previous video).

    Second, there is thrust play as well. It appears the shaft is centered by the blades, rather than by a thrust washer.
    https://youtu.be/XNirKF3UBYk

    The blades, are larger than the bore, or perhaps not round.
    IMG_4983.jpg

    The holes for the screws, also appear not centered with the holes on the shaft.
    IMG_5001.jpgIMG_5001.jpg
    IMG_5002.jpg

    I'm curious if this is normal. These are custom blades for this bored out unit.

    Right not, it appears at idle with the shaft on the stop screw, there was not much gap (0.03 mm plastic shim stock didn't fit). I'm not sure how the fuels getting around...it looks like there is a smaller gap in some areas, based on the wear marks on the bore.
    IMG_4986.jpg
    IMG_4984.jpg
    IMG_4989.jpg
    IMG_4993.jpg

    I used some 600 grit sandpaper to remove all the sharp edges and nicks from the edges of the blades. I will work to recenter them as best I can and find a thrust washer to reduce the axial play in the shaft. I may try preloading the spring a full turn more, or adding a secondary return spring, if those other improvements don't solve it. One frustration I have is the significant deformation of the AL blades, from the screws, prevents them from properly floating while you tighten the screws. Are all the blades in the stock units AL? or are they steel?

  2. #17
    Fuel Injected!
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    Didn't see that one coming. Time to yell at the machinist!!! Or be cordial and see what they will do for you. Oh...and I just took a magnet to couple of my OE units and yes, the blades are made of aluminum.

  3. #18
    Fuel Injected! Terminal_Crazy's Avatar
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    Don't Forget things heat up and expand when hot.
    Also there will be some flex on the shaft and wear on the throttle stop parts etc.

    If you open and slam the blades shut rather than carefully closing them shut do they stick any.
    It might only need a fraction of a degree turn on the throttle stop to just lift them off the body and stop them sticking.

    I recently had to adjust mine as it occasionally had a slight stick to it.

    Thanks
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  4. #19
    Fuel Injected!
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    I'd take a little off the blades where it appears they are heavily contacting the bore. The first picture right by the throttle shaft hole appears to be one spot. I don't recall stock butterflies having their edges rounded. I thought they were cut to match the bore angle when closed. If not that, then square cut.

    Overall, it looks to be an issue with the oversized butterflies not matching to the bore the same way a stock setup does.

  5. #20
    Fuel Injected!
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    Thanks everyone. I'm not interested in trying to work with the company that sold me this one, I had problems with the first unit they shipped me (cracks in the throttle shaft). And I had to pay to ship it back to them to get it fixed. And neither their old email nor their new on on their website work, they all bounce.

    The throttle doesn't stick when I let it slam closed. However I'd like this to be dialed in.

    I did take a bit off the blades where I noticed rubbing. Not much though.

    I'm going to the junkyard today to inspect how other units have clearances, etc. Then i'll work to replicate that.

  6. #21
    Fuel Injected! S.O.B.B.'s Avatar
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    If you are going to a yard look for 454 tb. Swap the whole thing or just use the blades if u'd rather use the unit you have. At least you could shave the blades to fit better with the holes as center to follow so they fit more like factory.if you trim or make another set just go slow.a tiny bit off at a time till you get it.
    Jeeper
    87 sjimmy powered by a 92 cadillac 4.9L pfi on 7427pcm /700r4/ 8.8 3.55 rear/disc brakes.

  7. #22
    Fuel Injected!
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    I don't know what I was searching for...I think it had something to do with the stock size bore and stumbled across this (from TGO)...
    Quote Originally Posted by RBob View Post
    I'd like to toss soemthing in here that may not be known. The throttle shaft is offset in the bore.
    The side of the butterfly upstream of the shaft has a larger area. This is so manifold vacuum tends to pull the throttle shut as opposed to open. So don't be surprised or think that the TBI is bad because of this.


    I believe Quadrajets have 2" secondaries if you need a butterflys. Gotta' be something good about having a carb laying around!


    RBob.

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