Throttle Sticking - any ideas for fixing?

[tony-baroni]

Here's a couple links to video's showing my sticking throttle. And a couple things that enable it to close properly.
https://youtu.be/kgT8Mum5fhQ
https://youtu.be/h1SSb0Gd38E

Quick symptoms list:
* Slow application of the throttle, causes it to stick partially open.
* Turning off the engine, allows it to close properly.
* Unplugging the MAP vacuum line, allows it to close properly.
* The throttle returns properly every time when engine is not running.

More Info:
This is not the first time I've had this problem. I've replaced MAP and TPS (twice) trying to get this to be fixed. None of those replacements fixed it. It's intermittent when driving...sometimes it'll have error codes. I suspect that it's frequently sticking, however under a load, and with the doghouse installed, I think I'm just not noticing it.

Last time it was fixed (summer 2015), my mechanic adjusted the TPS position to a lower voltage and that fixed the problem. I have NOT touched the TPS mounting screws since then.

Recently the engine was rebuilt and reinstalled. The problem reoccurred at that point. I've got ~800 miles on it, and the service engine light came on three times. Codes include:
42 Ignition Error
33 MAP sensor high
22 TPS sensor low


I asked for help with this before on a different forum.
http://tunerpro.net/forum/viewtopic.php?p=14808#14808

I can log info from tuner pro, I also plan to to check vacuum and TPS voltage when the vehicle is NOT running, and will follow up with a reply or edit this post with the findings.

General info:
1995 Chevy G30 HD van
CA Smogged - passes visual and sniffer (set base timing back to 0, from the Harris recommended 10deg for test)
350 TBI
Summit AL CARB legal heads (design similar to vortec...with improved geometry/flow around valve stems in chambers)
Stock exhaust manifolds
L31R short block w/ stock cam from a 1996
ECM: 16197427 BNKM
Modified bin (from Brian Harris)
Upgrades from Harris' recommendations...regulator spring, ultimate mods TBI, upgraded fuel pump.
~15k miles on upgraded TBI w/ larger bores/butterflies, modified gasket, and intake. The shaft and bushings are good, there is NO sticking, and the torsion spring is strong.

[tony-baroni]

TPS info
Tunerpro RT plugged into vehicle, looking for connection.
Turn key to ON.
TPS voltage displays 0.5, frequently switching between 0.4 and 0.5
TPS throttle position % shows 0% initially, but then starts creeping up, gage moves up/down by a few tenths, or points...after a minute it's fluctuating around 3-4%, wait a bit, now it's steady at 5.1%

Then V drops to 0.4, and TPS% fluctuates between 3.9 and 4.3%

pedal to floor, shows 4.6V, 100%
release pedal, shows 0.4-0.5V, 3.9-4.3%

Tapping throttle, not exceeding 10% throttle position, and V varies/jumps between 0.7 and 0.2V, let it sit.
V stabilizes between 0.2-0.3V, TP at 0.4-1.6%

Pulled doghouse, and unplugged TPS from harness. Connected tunerpro, and switched key to ON, engine still not running.
TP5 reads 0.0-0.1V, at 0%TP
TPS sensor is rigidly attached to TBI as I expected, no movement there.
Plug in sensor to harness, V jumps to fluctuate between 0.3 and 0.5V, and TP% jumps right up to 5%, and fluctuates.
I find that I can tap on the sensor itself, and the reading fluctuates. Is this typical with the sensors? I've got two from my mod'd TBI provider.

Also, I am getting continuous TUnerPro fluctuating between DA: Connected, and DA Data Error!

Any ideas on why that would happen as well? I've tried various USB ports, and it behaves the same.
I also tried turning OFF the connection within TP5, then turned off key, flipped TP5 connection on (status DA:Connecting...), and then turning key ON. No connection.
Toggle the connection on/off, no change. Had to reboot TP5 twice to get a connection.

[lionelhutz]

Bore for the throttle shaft worn out so the shaft has play in the hole? You can find bushing kits fairly cheaply if you search Ebay.

[tony-baroni]

Throttle shaft is a-ok...the TBI is as new - from SPR performance. Super smooth, no friction or binding.

[lionelhutz]

OK, didn't see it mentioned in your posts. It has to be a mechanical binding of some sort. The vacuum might be pulling the blades in the direction to cause a bind.

The TPS should not cause it if it's properly installed. The MAP sensor can't cause it.

[tony-baroni]

It is puzzling...I like where you're going with the vacuum pulling blades in a particular direction. I can't feel ANY sticking when moving the blades or the cable attaching bracket. I have taken a bunch more video's of diagnosing this...and will update with new links when I get them up on youtube.

FYI, I also had the throttle cable inspected by a mechanic back when it first occurred. I also checked it when I first had this problem with the new rebuild. There is no stiction in the cable.

[S.O.B.B.]

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.

[stew86MCSS396]

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)...

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.