Soooo, if the car is running the throttle body will stick anywhere from 5 to 20% open. Not good. In between gears that can potentially spin the motor past 5k rpm.

The damn thing only sticks when the car is running. Doesn't matter if it's a cold start or hot start.

The mere introduction of air zipping past the blade causes it to stick.

Return springs are good.

Loosened tps to make sure it wasn't binding the other side of the shaft.

Cleaned the inside of the throttle body. Lubed the heck out of it.

Lubed the outside points also.

The thing will ONLY stick while the car is running.

Crazy, eh?

Disconnect the throttle cable and detent cable. Start the car, and manually run the throttle to see if you can get it to stick. If you can't get it to reproduce the symptoms, try connecting the detent. Repeat, and if nothing still, reconnect the throttle. Repeat.

Could the cruise control system be malfunctioning? Does it have a third cable for cruise or is that controlled via the throttle cable?

I should've mentioned earlier that this phenomena is totally independent of the throttle cable. I've removed it and it with no effect.

Methinks the shaft or shaft bushings or whatever is in this thing are waaay worn out.

That's the next thing, the bushings.

I know a guy, a very talented machinist who rebuilds TBs, bores them, installs bearings on the throttle blade shafts, and installs new custom machined throttle blades that fit perfectly.

Not very expensive, I bought one several years back when I was going to do an LT1 topped 405.

If you're interested in having him send you a rebuilt one I will send you his info, and you can take it from there.

The engine vaccum is bending the throttle shaft slightly or otherwise tweaking it within the bushings or bore, giving it too much friction to close.

My stock unit and the 2 used ones I replaced them with all do this.

Here is my story. I have the AS&M monoblade on 355 modified TPI system. I drove it for quite awhile with no problems. Then from time to time the idle would not go below 1100 rpms. As time went by it would happen more frequently.

So I finally decided to investigate the cause. I noticed that the throttle body would stick open ever so slightly. I could easily manually close it and the idle would go down to around 775rpm like it should.

The next time this happened I confirmed the throttle was still open a little. I just shut off the motor and the throttle closed all the way. So I went to the hardware store and looked through their selection of springs and bought a light weight spring of the right size and length and installed it to help in the return of the throttle. The problem went away and has not come back. Easy enough fix.

By the way this problem also exist with other throttle bodies just not only the monoblade. The ones I have seen it on are usually high performance cars.

You guys are dead on about this thing.

My IAC is working fine. It allows enough air to pass through that if you put your finger over the bypass hole in front of the blade that you'll damn near lose the end of your finger.

I took the tb out of the car and doubly cleaned it with the toxic chemicals. Then I noticed there was a shiny spot on the body where the blade was gently rubbing. I sanded the crap out it for more clearance. Cleaned it again. Same problem. Ugghhh.

Tried a "purple" spring from a brake rebuild kit. Results bleh. Still sometimes allows the blade to stay open just a hair.

At this point, I'm thinking I may adjust the idle throttle set screw out a bit further and re-adjust the tps to compensate accordingly.

Btw, this is on a 401+ cid motor.

...remember your idle is actually controlled by the IAC and computer....too much air and the IAC runs out of control

..look very carefully, the TB probably is not going fully closed even when the engine is off...does not take much to let too much air in

...corrected similiar problem on my Edelbrock 58mm by simply bending the lever that connects to the blades to allow them to go a little more closed..

..fixed my problem

Another good point and potentially an easy fix.

Yes, the IAC is hitting way high count #'s and is allowing bypass of air. Unfortunately, it is not enough

Yeap, tb does go fully closed as soon as the key is off. Weird indeed though understandable if the thing is sucking through mega atmospheres of air.

I did think it was totally cool that the open faced K&N element could be heard outside the car at idle... now I'm thinking it's not so cool. Though, the tb stays open with or without the accordian hose connector. Mega air. Just gotta deal with it I suppose.

The more you open the throttle blades with the screw, the IAC steps should come down. Open it up till the IAC steps are in the single digits, then see if the problem goes away. The more you are closing it and making the IAC steps go up, it is forcing alot of air in through a small passage and actually pulling harder on the monoblade.

If the above still does not work to solve your problem, just put the throttle adjustment screw back to where yo have about 20 to 30 IAC steps at warm idle, then run a really heavy spring, or put a lever of sorts down to effectively extend where the spring hooks to the throttle body, giving it more leverage. You need to make the spring have enough power to overcome the suction of the motor. You will then need a heavier foot to drive the car.

Another thing I have heard of, though I have no experience with it so you should talk to someone who does before trying it if you don't have an extra throttle blade, is to drill a couple small holes in the blade to let air come through. This should let you close the blade more and still keep the iac steps down as some air will be coming through the holes. If the holes are positioned right and sized right it keeps the blade from being open at all at idle and helps keep it from being sucked open. I think the holes should be drilled on the same 1/2 of the blade that is being sucked open, which would be the bottom 1/2 on mine though I haven't seen yours. Would be 1/2 way between the lower edge of the blade and the center pivot rod. Maybe 2 holes, 1 towards each side. But I'm not 100% sure on that, do some searching on other sites or ask someone else exactly where is the best position for the holes. They need to be sized so that the blade is prettymuch completely shut when the car is idling. Start with fairly small holes, adjust the idle screw so the IAC steps are 20 or so, and try it. If you still have the problem, go a little bigger with the holes, re-adjust back to 20 or so iac steps, try again.

Sounds like you need to either recalibrate the TPS (throttle position sensor) or the throttle cable needs to be readjusted.

Shouldn't have to drill any holes in an AS&M Mono Blade to get it to idle.

My car idles at 980-1100RPM with the idle screw barely 1/2 turn off full close. Now I had to drill one .100 hole in each blade of my 58mm TB to make my car idle without the blades opend up 1/4".

My Mono Blade works perfectly, and it is the only one I have ever fooled with. I know alot of folks have problems with the Mono Blade getting hung up and their motor is stuck on "high idle" when driving. I thought that phenomon was only on forced induction cars thou....

If I were you - I would check the alignment of the throttle blade in the housing and make sure it is centered properly. Make sure the screws holding the blade to the throttle shaft are tight and the blade is tight on the shaft. You stated it was rubbing the bottom of the housing... that is the first indication that one of the above is wrong. Find out why it is touching the bottom of the housing, putting screen door closer springs and sanding the housing is just masking the real problem.
Will

Disassembling the shaft and blade told the tale, unfortunately.

Surprisingly enough, there was a hairline crack through the shaft on the manifold side

That hairline break was enough to allow the blade to distort out of alignment.

Next question is: Any way to get parts for the Arizona Speed and Marine units?

Edit: just did a quick search for Arizona Speed and Marine. Guess I'll try calling them on Monday to see if they offer a rebuild service. I must've bought my original one 10+ yrs ago. It couldn't hurt to have the the brass bushings replaced for the shaft too.

I'm sure they'd be glad to help you (for a fee!). I'm sure they'd be interested in the failure at least. Look on the bright side, your engine didn't ingest any metal bits.

You have that right! Thankfully none of the blade screws came loose.

I did talk to Arizona Speed and Marine. They are making up a batch of new shafts and do have the end bushings. For a small fee of $68 I'll be back in the sweet spot of max air-flow.

The 58mm that I have in there now is definitely restricting the motor. The seat of the pants dyno says that rolling burnouts don't happen as easily as they did with the monoblade.

"The 58mm that I have in there now is definitely restricting the motor. The seat of the pants dyno says that rolling burnouts don't happen as easily as they did with the monoblade."

Interesting to know. My theory is a bigger throttle can't hurt anything and may help depending on the mods.

I tried switching the two throttle bodies with the 350cid motor (heads/cam, everything else) and don't remember any difference whatsover.

With the big cube motor-- yes, it definitely needs to breath.

While driving and watching the trims, it was obvious the monoblade was allowing more air into the motor because the BLM's were headed more higher