Help! Dropped bolt down intake manifold

All right, ready for something stupid? Took the M out for a test drive to get it up to 40-45. Got up to speed running well then took my foot off the pedal and the throttle did not let up. I reached down and pulled the pedal up, still no decel, so I shut the engine off.

Look under the hood and, long story short, the center stud from the stupid non-stock air cleaner that was on there seems to have fallen down the carb throat. I took the carb, spacer and governor off and couldn't find anything and can't see anything in the intake housing, but I'm pretty sure it's in there.

The symptoms are that as soon as you fire the engine up, it's running at full tilt. I had to crank out the idle screw and choke it severely just to get it home. What's going on here? Why is it getting so much air (or maybe little to no gas) if something's in there?

I'm going to take the manifold off and have a look. I don't think anything is ruined as the engine sounds fine, it's just running at full tilt. Ugh....

Got the intake manifold off and haven't found anything yet. I'm afraid it's slipped into the engine side of the intake. Is there any access into that side of the intake? It doesn't look like I can get to it from the top.

Any ideas would be very helpful. I think I'll try and fish a coat hangar in there and see if I can find anything.

If the bolt isn't caught in the throttle plate, then that wouldn't be causing the high idle. Anywhere downstream of the carb would do one of three things:

A) Cause a loud knocking noise

B) Cause some major damage (especially if its a 1/4" bolt like most air filters use)

C) Hold an intake valve open causing a miss.

I'd disconnect the throttle linkage first and be sure the throttle plate is closing fully.

If it did in fact ingest a bolt, by now it either went through without any problems, or should be in one of the intake runners or the head. A magnet should be able to retrieve it if you can get to it.

I know it may sound elemetary, but does your truck have a throttle control on the dash above the gas pedal? Be sure its all the way home by turning it and pushing it all the way in.

Yeah, I can't figure out why it would cause the high idle. There is no knocking and damage that I'm aware of and it's not missing. This thing was like 3-4 inches long, I can't imagine it could've gotten far.

I think I'll try a magnet.

One thing I just noticed, while I have the carb off, I pulled the throttle all the way open and the throttle plate goes past straight up and down. I would think that all the way open would result in the plate being straight up and down, at best, maybe even more closed than that. It surely shouldn't be past vertical so that it starts closing again. And with the throttle completely closed, the plate ought to almost close the entire hole, right? It's probably 1/4 of the way to vertical when the throttle lever is all the way down.

I'm thinking that stupid stud somehow twisted that plate or the rod in the throttle lever. It would make sense that that would be adjustable with a retaining screw or something. I'll check it out.

Still doesn't tell me where the stud went.

If the stud caught in the right position, it could have bent the throttle plate for sure. That would account for it not closing all the way. With the linkage all the way down against the idle screw, it should be closed almost completely. You may see a little light around the edge of the plate with the idle screw adjusted properly, but no more than maybe .020" give or take.

Is there a chance the outside linkage moved on the throttle shaft? I'd look at it closely.

If the throttle plate were bent, I would also think you'd see some sort of marks on it from the stud.....

Quote:

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Originally Posted by randyscycle

Is there a chance the outside linkage moved on the throttle shaft? I'd look at it closely.

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x2

The stud most likely began to fall and became wedged. When you applied pedal, it jammed causing the throttle linkage to slip or bend and also bent your throttle plate. Do you recall a stiff pedal at any point? Sounds as if you were test driving with no air cleaner and just the stud in the carb if I am inferring correctly. I'm guessing the stud is history on the side of the road in that case and you're simply at the point of unbending everything and you'll be home free. Many of the studs on aftermarket cleaners will spin at idle if the wingnut isn't there to torque them in place. I really don't think your engine ingested it.

Success!! I found the world's most useful tool at O'Reilly today. It's a magnet/LED light on the end of a flexible shaft, $10. I got home and stuck it in the intake runners and about 2 seconds later I hear a "clink!". Pulled it out and sure enough there's the stud. Man I'm glad I got that outa there with no damage.

http://img374.imageshack.us/img374/9827/img009pb5.jpg

As far as the carb, yes, the throttle plate was bent. It was open about 1/4" with the throttle lever completely down. A few seconds with some pliers fixed that. Once, I finally got everything together, it ran like new. Thanks for all the help and ideas.

Glad you lucked up and got to the stud before it got to the engine!

Yep, luck was on my side for once. I attribute it to clean livin'. :)

In reality, and I'm not sure exactly what the runners look like, but I'm guessing the bolt was too long to make the last turn into the valve. Probably could've stayed there forever. Glad it's out, though.

Definitely glad its out!

I like the tool you found too. I just may have to pick one of those up. As the eyesight gets worse and the reach gets less, I can see that having some real value under the hood.....:D

On another note, I had a 396 Chevy that I drove around for years with a bolt in the oil pan. I knew it was there, dropped it in while I had the intake off. It was of course too big to go through the pickup screen, so I figured it'd be heavy enough to not ever get out of the sump. Never had a problem because of it.