I installed a monoblade on my '92 supercharged L98. I know it is overkill for it, but I got a good deal when I bought it with a miniram. I put it on my stock plenum and manifold, and it sticks. The idle will not go below 1500 no matter what I adjust it to, then it will stick at 3 or 4,000 out driving it. My thought is maybe the boost is holding it open. Any ideas or anyone who wants to trade for a 58mm?

 

I would check it physically while off the car.. then make sure that the plenum where it bolts to is opened up properly , clearanced and that when bolted to the plenum, the alignment is such that the edges are not catching anywhere.. this would be my first thought on it.. the second is to make sure the linkage arm is free and clear and that the spring is wound tight enough to return it to a closed position.. once all these are checked, if it still persists, you need to contact the manufacturer and see if they will take it back and make sure the center rod is not bent causing it to open and shut irregularly. also may wanna check and make sure the throttle cable is long enough and not being stretched to a point where it is not allowing the TB to close and seat all the way.

Chris

 

I have the exact same throttle body on my car. I had both of the problems you've described. As far as not idling below 1,500 rpm, reach down with the car idling and physically close the throttle by grabbing the black composit piece that mounts the throttle cable. I took mine off and drilled a very small hole through the composit member and the metal piece positioned right behind it (Be careful where you drill your hole as to not interfere with throttle movement). I then tapped the underlying metal piece that is supposed to ride in unison with the throttle cable carrier. My metal piece would just barely move independently of the composit member since it wasn't totally tight on the shaft which runs through the throttle body carrying the mono blade. I absolutely believe this is a design defect! Once I anchored the throttle cable carrier to the metal piece right behind it I no longer had that problem. I tapped the metal piece used a correspoding bolt, used loctite, and sanded the threaded end of the bolt down as to be flat with the metal piece through which it extends.

As to the sticking at partial throttle. All I can say is I really had to back off of my blowoff valve to keep this from happening. I know exactly what you are talking about.. the car wants to keep accelerating and the throttle sticks for a brief moment. Back way off on your blow off valve and see what happens. I wouldn't trade the throttle body if I were you. If you want to move huge air it's the only way to go.

Tony

 

Tony,
Could you clearify what you meant when you said "back off of my blow off valve" bacause I'm having similar problems with my TB.
Thanks,
CT

 

Back off on the spring tension. All you need is just enough to keep the blow off valve shut when manifold pressure drops in your manifold. Remember, you will have the exact same pressure trying to keep the blow off valve shut under boost as is trying to blow it open (the boost itself). So, the spring that holds the valve against the blow off seat makes up the difference to keep the blow off valve seated under boost conditions. If your spring is too tight after you let off of the throttle under boost conditions it will take an instant too long for your manifold to see vacuum (we are talking about spilt seconds here) again. It is the vacuum that allows the blow off valve to open thus relieving pressure from the system. The less pressure you have on the spring the sooner it will open after you let off of the throttle since it won't take as much manifold pressure to open it.

Hope that helps,

Tony

 

Got any pics of this?

 

Thanks!

 

I had the same problem with my ASM 58mm TB. It took me a while to figure out that the plastic piece with the cable, and the metal piece with the throttle stop, were not locked together. While it was idling high, I pushed down on the plastic part and it moved, even though the metal part was against the throttle stop. I just dripped some super glue between the metal and plastic, and let it sit overnight. It seems to be holding so far, but I was planning on drilling a hole like you did, and either putting in a screw or a small cotter pin.

Darren

 

I wouldn't trust the superglue as a long term solution. A cotter key or roll pin probably won't work because the the cross section of the two pieces together is too small to hold a roll pin or cotter key. I think a small bolt with loc-tite is the only way to go! I do not have any pictures of how I fixed mine, but it is really easy to do. Just bolt the two pieces together in a manner which does not impede throttle movement. My bolt is above the rotation shaft but fairly close to it. In other words, you can see the bolt I added my looking at the top half of the throttle cable carrier from the side.

 

 

I really can't get a good picture of it since I have a water pipe that runs RIGHT next to it. Trust me, it's a simple fix.

 

Well after my previous comments of not having this happen to me, it has happened (last night). The part about the car wanting to accellerate during a shift is a PITA. If I shift at 6K, it will hit the redlight (6.5K) even after I let off the gas. The first time it happened, I killed the motor at redline due to I thought I had a stuck throttle (scary!!!).

I will have to investigate the screw thing on the BO valve. I was also wondering if this could be an issue by how much is routed off this single vacuum source. I have the vacuum fed off the back of the intake, and it feeds the MAP (~1" from source), boost guage (~6" away from source), the FPR (~24" from source), and the BO valve (~6' from source).

Additionally, I have ran another MB in the past and not had that issue, and just recently was running an Accel 58 billet TB with no issues.

Thoughts?

Aaron

 

I would absolultely have a dedicated vacuum line for your blow off valve. That way if one of your other vacuum lines cracks that is on the same inlet as your blow off valve, it shouldn't cause such a problem.

 

I still have not solved the MB sticking issue. Under accelleration, if I shift at 4K, the RPM will stay at 4K until I hit the next gear. If I am cruising at at 2200 RPM the idle will just stay at 2200 (like cruise control), until you quickly rap the throttle. Then it will settle back to 875 RPM (idle setpoint). I have adjusted the BO valve out a full 8.5 turns to date (seems to have no effect on this issue). I wonder if I should try going some amount in from the original setting to see if it helps.

I am having so much difficulty that I am considering swapping to a spare MB that I have sitting. The problem is that the 2nd MB is painted yellow vs the one on the car now is powdercoated, and they are not a perfect match. If I still have the issue, I am going to throw one of the 58 billets back on that I know have not had this issue.

My throttle blades are not moving independent of the throttle lever (at least as far as I am able to tell.

If you rev the car in the garage to 2500 and let off, the idle takes a second or two to settle back to the idle level. But the throttle lever stays right where it was when you let off the throttle. The TPS appears to go back to 19% (idle setpoint in FAST) as soon as you release the lever, indicating the blades appear to be closing.

I'm stumped at this point. And this car is very dangerous to drive like this. Imagine your throttle stuck in every gear, no matter wher you shift.

Aaron

 

If it were me I'd say screw it, bust out the TIG and modify the manifold for a nice LS1 round billet 90mm.

 

Yeah, yeah, yeah!.

If only it wasn't already fabbed and on the car. For us L-98 guys, we still have to have a waterneck, which requires the shorter TB.

I am really bummed about the situation. A lot of time and work has gone into this package and to have a TB issue holding up progress.

The MB was used and had been smacked on the end during transit (hard enough to bend the TPS sensor bolts), but everything appeared to move as designed. It snaps shut without issue.

Aaron

 

I feel your pain bud. I dont think any of us go thru a major project without having at least one thing, ususally a simply thing screw the whole deal. Like a fly in the cakemix. at this point I am wondering if the oval blade is being affected by dynamic pressure. Perhaps slighty offset? Bent shaft? Bearing not seated true?
I know it's laim, but havee you tried some Honkin' return springs? (just to rule it out)

 

Since the mono blade is so large, I do know that it doesn't take much as far as not seating to make a large difference in idle speed. Are you using a supercharger/turbocharger? If so, you blow off needs to be VERY lightly tensioned..

 

The air lift idea (throttle blade acting like a wing in the airflow channel)has been discussed, but it would seem that all of the big boost cars would be having this issue if that was the case. I have tightened the throttle return an additional 1/2 turn to get more tension (this required drilling a new hole in the throttle lever to allow the "tang" to pass through). The throttle blade has a lot of tension, even more so than any previous throttle body that I have run in the past.

With regard to the application, I am running this on a FI application, but the boost does not apply at the lower RPM, or just very slight throttle openings. I have backed off the BO valve 8.5 turns; to the point, that the screw feels like it is about to fall out. You were saying back the screw out, not turn it in? Right?

Thanks for the replies.
Aaron

 

Yes, how big is your bypass valve? Maybe you need a larger one.