Throttle body uh-oh moment...

[Great White]

On Saturday my lady and I went out for a long day of driving on a charity cruise for a friend of hers who passed. I got a solid 5 hours of windshield time in. The drive was a blast but I experienced an issue a couple times where the throttle body wouldn't let me push the accelerator pedal past opening the primary throttle plate. It took considerable force, and once was able to open the secondary plates they opened very abruptly. It only happened twice.

This will be a fun thing to repair methinks.

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[Paul Workman]

Cable or the TB itself... Hope it is something simple (DIY/cheap).

[Jagdpanzer]

Sounds like is binding up somewhere in the throttle body linkage. The primary throttle is actuated by a cam attached to the secondary shaft. The throttle cable rotates the secondary shaft which rotates the cam against the primary throttle shaft follower. After primary is fully opened the linkage begins to open the secondary throttle blades. Sometimes the contact area between the cam and primary shaft follower becomes worn to a point where it prevents a smooth opening of the secondaries. This can be easily investigated by removing the throttle body linkage cover to see where the hang up is occurring.


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[Great White]

I finally got a chance to disassemble, clean, and evaluate the throttle body. This is what I've found. It appears there is more than one issue. The pin on the end of the primary throttle shaft has some flats worn into it. The bores it lives in on the throttle body are worn enough that it has a considerable amount of play. The last thing of concern to me is the groove that has been worn in to the driver's side secondary throttle bore by the plate on that side. I'm a little surprised there is no off-throttle stop on these (nor any cushion.) The plates just rest against the bore when the throttle is released.

I'm going to try to smooth some things out on it. I might even end up making a new pin for the primary throttle shaft.IMG_20210919_0003190.jpgIMG_20210919_0002133.jpg

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[Mikey]

Sounds like the secondaries are sticking to the bore. Careful in your smoothing process, don't go overboard and ruin the ability of the blades to seal or else you'll get air leakage past the blades when they are otherwise supposed to be closed.

[Jagdpanzer]

You can rotate the pin on the primary shaft to fresh unworn contact area. Grip it with Jacobs chuck and rotate the lever with a small crescent wrench. While at it polish the cam area that contacts the pin.


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[Great White]

Upon further inspection of the throttle body, the wear on the pin wasn't the issue. I elected to leave the pin alone and instead concentrate on the throttle bores and butterfly plates where the sticking was occurring. I bought a cylinder hone and was able to remove the grooves in the throttle bores without removing much material. (Maybe around .005" or so from the diameter.) After honing the bores I used some sand paper and metal polish to clean up the edges and re-fit the butterfly plates to their bores. They're not a perfect fit, but it's a lot closer. Most importantly, they no longer stick!

While re-assembling I used red loctite for the screws, and put dry graphite on all the wear-points.IMG_20210919_1820358~2.jpgIMG_20210919_2139298.jpgIMG_20210919_2139479.jpg

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[Mikey]

Glad you were able to fix it easily! Exactly as I had suspected.

[Great White]

Don't get the wrong idea; it was pretty tedious and time consuming. It ate up what little free time I had this past weekend. It wasn't necessarily difficult unless you're impatient (which I've been accused of before.) I got it put back on the car last night and it seems to idle correctly. No hang-ups or sticking. I think I lucked out getting the TPS in the right spot.

I wasn't able to pull the car out and do a proper road test though because of the weather outside. Not sure how much rain we got but it was plenty for my taste.

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[Mikey]

Time consuming doesn?t factor on any difficulty rating in my book. However I do hope you don?t come to regret using red loctite in an unnecessary way.