454 Sticky Throttle is a death trap

[thinger2]

That is a mechanical problem.
Worn throttle shaft, cruded up throttle bores, throttle plates sticking when hot.
High hot idle because the throttle wont close.
Pulling air through the worn throttle shaft bushings when at idle.
Bad base gasket. Etc.
Rebuild the tbi and replace all of the vacuum hoses.
Clean the EGR and all of its ports and passeges.
I know better educated guys than me will show up but I just dont believe that a 89 ECM has any way to make the throttle stick open.
I think you have a entirely mechanical set of issues.
Stuck, worn throttle likage, bad cables. etc..
Dont be so quick to discount the guy who mentioned bad motor mounts either.
Back in the early 70s, The biggest recall in history was from motor mounts.
This is why we have "caged mounts"
They are designed to hold the engine in place if the mount seperates.
If you break an uncaged mount on anything before about 1970 or so the torque of the engine will rotate it and pull the throttle wide open.
It pulls the pedal right from under your foot and slams it on the floor and chucks you in the back seat.
The only thing you can do is try to shut it off.
Hard to do when you are in the back seat.

 

[someotherguy]

When I broke the driver's side mount on my '63 Suburban (w/350 and TH400 swapped in), if you floored it, it would lean the engine over and knock it out of gear. Coulda been worse..

Richard

 

[Schurkey]

Back in the early 70s, The biggest recall in history was from motor mounts.
This is why we have "caged mounts"
They are designed to hold the engine in place if the mount seperates.
If you break an uncaged mount on anything before about 1970 or so the torque of the engine will rotate it and pull the throttle wide open.
It pulls the pedal right from under your foot and slams it on the floor and chucks you in the back seat.
The only thing you can do is try to shut it off.
Hard to do when you are in the back seat.

More-or-less true.

Chevy, for example, used to use a throttle linkage rather than a throttle cable. The usual scenario was some ol' lady or other "senile citizen" making a left turn from a stop on a busy street. They'd stab the gas pedal intending to swiftly merge into traffic. The engine torque combined with centrifugal force from the left turn, would lift the engine off the broken left-side engine cushion. As the engine lifted, the throttle linkage would pull the throttle open--increasing the torque, which increased the engine lift, which opened the throttle even more. At some point, the engine lifted high enough to rip the vacuum hose and check-valve out of the power booster, essentially disabling the brakes for the lil' ol' lady driver. She's now got an out-of-control car with "no brakes" spinning donuts in the middle of a busy road until she crashed into something or someone.

The senile citizen would freeze--or panic--or both. Sheetmetal was rumpled, folks got injured or killed.

Rather than fix the crappy, weak, broken motor mounts with something stronger, GM added a $5 steel cable and bracket assembly that tied the exhaust manifold bolts to the control arm cross-shaft. Didn't stop the crappy motor mounts from breaking, but it did prevent the engine from lifting beyond what the steel cable would allow.

 

[sewlow]

More-or-less true.

Chevy, for example, used to use a throttle linkage rather than a throttle cable. The usual scenario was some ol' lady or other "senile citizen" making a left turn from a stop on a busy street. They'd stab the gas pedal intending to swiftly merge into traffic. The engine torque combined with centrifugal force from the left turn, would lift the engine off the broken left-side engine cushion. As the engine lifted, the throttle linkage would pull the throttle open--increasing the torque, which increased the engine lift, which opened the throttle even more. At some point, the engine lifted high enough to rip the vacuum hose and check-valve out of the power booster, essentially disabling the brakes for the lil' ol' lady driver. She's now got an out-of-control car with "no brakes" spinning donuts in the middle of a busy road until she crashed into something or someone.

The senile citizen would freeze--or panic--or both. Sheetmetal was rumpled, folks got injured or killed.

Rather than fix the crappy, weak, broken motor mounts with something stronger, GM added a $5 steel cable and bracket assembly that tied the exhaust manifold bolts to the control arm cross-shaft. Didn't stop the crappy motor mounts from breaking, but it did prevent the engine from lifting beyond what the steel cable would allow.

On my BBC Nova, I swapped out that cable for a turn-buckle, along with some solid engine mounts.
Big HP, big torque, a 4-gear & throttle linkage, in a uni-body. A recipe for disaster.
Yea, I had it stick on me once. Right after was when all was upgraded.
Have to remember when that happens, don't turn the key too far when shutting it down.
Locks the steering!
"Holy schnappin' arseholes, Batman!" Surprise!

 

[thinger2]

More-or-less true.

Chevy, for example, used to use a throttle linkage rather than a throttle cable. The usual scenario was some ol' lady or other "senile citizen" making a left turn from a stop on a busy street. They'd stab the gas pedal intending to swiftly merge into traffic. The engine torque combined with centrifugal force from the left turn, would lift the engine off the broken left-side engine cushion. As the engine lifted, the throttle linkage would pull the throttle open--increasing the torque, which increased the engine lift, which opened the throttle even more. At some point, the engine lifted high enough to rip the vacuum hose and check-valve out of the power booster, essentially disabling the brakes for the lil' ol' lady driver. She's now got an out-of-control car with "no brakes" spinning donuts in the middle of a busy road until she crashed into something or someone.

The senile citizen would freeze--or panic--or both. Sheetmetal was rumpled, folks got injured or killed.

Rather than fix the crappy, weak, broken motor mounts with something stronger, GM added a $5 steel cable and bracket assembly that tied the exhaust manifold bolts to the control arm cross-shaft. Didn't stop the crappy motor mounts from breaking, but it did prevent the engine from lifting

When I broke the driver's side mount on my '63 Suburban (w/350 and TH400 swapped in), if you floored it, it would lean the engine over and knock it out of gear. Coulda been worse..

Richard

The drummer for our crappy band had a 69 charger with a column auto and a bad motor mount.
We all told him to stop standing in front of that damn car a revving it by the carb.
We told him it was gonna ******* hit him.
That was the night before halloween 1986.
I left the party early to go to a different party.
That cammed busted motor mount charger dropped into gear and pinned him between the front bumper and the back bumper of a jeep grand wagoneer.
Then it bounced back and hit him again before it stalled.
Snapped both of his legs right below the knee caps.
The guy standing next to him when this happened tried to jump out of the way but got his thigh pinched between the fender of the charger and the bumper on the jeep and it blew all of the muscles out of his upper leg like popping a zit.
They all gathered together and tracked me down and decided that I was driving that Charger home based on my experiance with driving broken motor mount cars.
If you never driven a cammed carb car with a broken motor mount.
Dont try to tell me all about it.
All of your theories and maybe coulda woulda do not matter when the throttle pulls wide open and you are laying in the back seat and cant reach the key.
Tell me all about it.

 

[thinger2]

On my BBC Nova, I swapped out that cable for a turn-buckle, along with some solid engine mounts.
Big HP, big torque, a 4-gear & throttle linkage, in a uni-body. A recipe for disaster.
Yea, I had it stick on me once. Right after was when all was upgraded.
Have to remember when that happens, don't turn the key too far when shutting it down.
Locks the steering!
"Holy schnappin' arseholes, Batman!" Surprise!

If you want real armour - all the seat action, bolt a hilborn injected methanol 427 chev into the fuel rotted stringers on a 7 liter wood hydroplane and have that torque out at 6500 rpm.
It leaves and takes most of the ass end of the boat with it.
Doesnt even say goodby.
No card no nothing.
And then they fish you out of the lake and your soon to be next ex wife throws things at your head and the kids are hiding in the background knowing that christmas just flipped upside down.
Wives and kids are just ungratefull.
They dont seem to understand how hard it is to recover from a head injury while you are trying to build a new boat and a new engine at the same time.
Its almost like they dont want to go racing anymore.

 

[Schurkey]

Uhgggg. Reminds me that the left stringer in my boat is black with rot.

I've been trying to forget that for years.

 

[PlatonicSolid]

So the 89 GMC C3500XC 7.4L recently developed a stalling at idle issue - only while in gear. No blinky light error codes. Really annoying when at a stop sign. I had previously replaced the TPS (as stated earlier in this thread) which was annoying as 1 of the screws broke in the process. No vacuum leaks evident, though I should probably replace all the little hoses - haven't searched to see which the vacuum parts are still purchasable. I reluctantly decided to clean the IAC - I say reluctantly as I expected the screws to break ... and they did not disapoint - both screws broke. The bonehead that designed this should be punished - Any engineer worth anything knows you don't use fine threaded steel screws in aluminum. Since I now have to remove the TB to fix the screw problem I decided I'd rather just buy a whole new TB. I quickly learned that for some strange reason you can't buy a new or aftermarket or remanufactured TBI-220 for a 1989 454 anywhere. What's up with that? Why is the TBI-220 for a 1989 454 "special"? I did luck out and found the exact rebuilt model 17089092 on ebay for $700 +tax +shipping and bought it - we'll see how that works out when it arrives. Kinda pricey, but as far as my search goes, there are no options.

As far as the IAC that I removed is concerned, it looked fine - likely OE. The silicone O-ring had seen better days = no flexibility and it has turned almost white with age.

 

[Schurkey]

So the 89 GMC C3500XC 7.4L recently developed a stalling at idle issue - only while in gear. No blinky light error codes.

Time to get a real scan tool. Blinky-light trouble codes are two steps away from madness.

I should probably replace all the little hoses - haven't searched to see which the vacuum parts are still purchasable.

None of the vacuum hoses are likely to be available. Make your own from generic vacuum tubing. As for the vacuum solenoids and such, expect to re-use the ones you have, or get "new-to-you" pieces from the Treasure Yard.

I'd rather just buy a whole new TB. I quickly learned that for some strange reason you can't buy a new or aftermarket or remanufactured TBI-220 for a 1989 454 anywhere. What's up with that? Why is the TBI-220 for a 1989 454 "special"?

I expect it's exactly the same as other "big-block" TBI units of similar model years...with differences in the vacuum hose plumbing. Some vacuum ports drilled and fitted with nipples, some ports unmachined.

A clever rebuilder drills ALL the ports, and sells "universal" TBI units; any un-needed vacuum nipples get plugged with caps.

I did luck out and found the exact rebuilt model 17089092 on ebay for $700 +tax +shipping and bought it - we'll see how that works out when it arrives. Kinda pricey, but as far as my search goes, there are no options.

Fookin' WOOF. $700 is beyond what I'd give. I'd go to heroic lengths to fix the one I had.

OTOH, Big-block TBI units don't grow on trees. And the Holley "replacement" TBI units for V6 and small-blocks are over $800 now, and thats if they're even available. Summit shows them as "not in stock" or "will be special ordered for you" but I bet they're discontinued.

Example:
www.summitracing.com/parts/hly-502-6

Holley 502-6 Holley OE Replacement Throttle Bodies | Summit Racing

Free Shipping - Holley OE Replacement Throttle Bodies with qualifying orders of $109. Shop Throttle Bodies at Summit Racing.

www.summitracing.com

 

[PlatonicSolid]

The Ebay rebuilt TBI worked fine, even if it didn't solve the problem. For anyone seaching for a TBI-220 17089092 in the future, after spending way too much on Ebay, I found it available on RockAuto at a much better price.
Notable is the very high pitched sound I hear which must be a vacuum leak and the likely source of the idling problem. I guessing the only way to replum all these hard plastic with rubber end vacuum lines is to remove them all and just use standard neoprene vacuum hose. I don't see the right angle rubber connectors available other than the 4 piece Dorman variety pack which means you pay $6.79 for the 1 you need x however many are in there + the straight ones have similar "variety packs".