454 Sticky Throttle is a death trap

[Scooterwrench]

Like shurkey said,just use bulk hose to make up your vacuum hoses. Don't try to make the bends too tight or they will kink. May not be as pretty as the formed plastic/rubber hoses the factory put on there but they will function just fine.

 

[PlatonicSolid]

Replaced almost all the vacuum lines. The one I didn't replace goes from a small nipple on the front of the TBI to a larger nipple on some small black box electrical thingy. Not sure the best method of changing from a small to larger nipple.

It may not matter since the performance didn't improve at all. Still stalls when idling in gear. It actually stalls idling in park now too when it's warmed up. Seems to idle in park OK when it's cool.

After driving it about 30 miles, which was an adventure = hold gas with right foot and brake with left foot at stop lights, it's now giving a code 44 = lean fuel possible O2 sensor.
This makes perfect sense since the exhaust flange leaks quite a bit. I sprayed the threaded flange studs and nuts with penetrating oil, but I'm wondering what the odds are of replacing the pipe flange gasket without breaking the flange studs in the exhaust manifold. If the studs break I'm screwed. I'd love to replace the studs as they look pretty bad, but this process looks like a nightmare. Not exactly easy access up there. Thinking this job might be best done in a garage with a lift.

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[Scooterwrench]

Replaced almost all the vacuum lines. The one I didn't replace goes from a small nipple on the front of the TBI to a larger nipple on some small black box electrical thingy. Not sure the best method of changing from a small to larger nipple.

It may not matter since the performance didn't improve at all. Still stalls when idling in gear. It actually stalls idling in park now too when it's warmed up. Seems to idle in park OK when it's cool.

After driving it about 30 miles, which was an adventure = hold gas with right foot and brake with left foot at stop lights, it's now giving a code 44 = lean fuel possible O2 sensor.
This makes perfect sense since the exhaust flange leaks quite a bit. I sprayed the threaded flange studs and nuts with penetrating oil, but I'm wondering what the odds are of replacing the pipe flange gasket without breaking the flange studs in the exhaust manifold. If the studs break I'm screwed. I'd love to replace the studs as they look pretty bad, but this process looks like a nightmare. Not exactly easy access up there. Thinking this job might be best done in a garage with a lift.

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Yeah those are pretty crusty but I've been able to get them off without breaking the studs. Fortunately the studs increase in dia. above the nuts.
This job is going to require a torch to heat those nuts red hot then carefully apply gradually increased torque till the nuts break loose. Stop and let cool a little until PB Blaser doesn't just smoke off when you spray it on there. Let it soak in then wet it again. You will probably have to work the nuts off by backing them out until they start to bind,re-wet,run them back on and repeat until you have worked them off. Bad thing is it looks the threads below the nut are almost gone. Hopefully you still have enough threads where the nut sits to hold it all together when you re-assemble. NAPA used to sell stud kits with the studs,springs and nuts. I recommend at least using the nuts and springs. I think your springs are toast too. To replace the studs you will have to heat the ears on the manifold red hot and repeat the process for removing the nuts.
Getting those nuts off will REQUIRE a six point,deepwell socket.

 

[Scooterwrench]

Oh yeah,
Get that wiring harness away from that manifold or you'll be walking eventually!!!

 

[thinger2]

Hi All - New here - first real post.
The patient: 89 GMC C3500XC 7.4L RWD AT Stock - Jasper engine installed 2007 - Truck purchased new by my parents
It has many issues that I can live with since it's just a utility vehicle for me (radio and clock no longer function, intermittent wiper control only works sometimes, brake warning light is usually ON - had 2 different mechanics try to fix this and both failed, but brakes work fine)

Symptom: Throttle sticks high. I'm going 40 MPH on flat road without stepping on gas. Have to put in neutral while driving and kick it to return to normal idle. If I only tap the gas it will stick at even higher idle. After initial warm up in the driveway, everything is fine = settles to normal low idle. Once I start driving it settles at higher idle until I kick it down (stop sign approaching - put in neutral - kick it down - stop at sign. Repeat constantly during journey = it's basically undriveable)

I can reproduce this at the throttle body. Makes me want to put a spring on the throttle to pull it back. Throttle moves smoothly with engine off, thus i believe throttle cable is fine.

Possibly related:
O2 sensor code 44 (using flashy light method) - Don't have a code reader, but would like to get one (guidance on what to get appreciated)
Exhaust leak at flange after O2 sensor - Just noticed that yesterday

Attempts to fix throttle issue:
Replace TPS and set to 0.61V per included instructions - made no difference
Disconnect Cruise Control at TB - I never use it and don't trust the wring in the steering column as it's part of the same stick as the erratic wiper control - made no difference

Best Guess at next step:
Figure out how to fix the exhaust flange leak in hopes that maybe O2 sensor is causing throttle issue.
If that doesn't work - replace IAC

Insight appreciated

That is a mechanical issue somewhere between the pedal and the throttle plates in the tbi and this also applies to carbs just in general.
That linkage may work just fine when you move it by hand.
Because you cant really feel if it is binding or not.
When it is running atmospheric pressure and vacuum are the forces involved.
And heat.
I think you have a binding throttle shaft or sticking throttle plates in the bore.
The allowable slop on the throttle shaft is pretty much zero.
You have a mechanical throttle linkage problem somewhere.
I dont know of any ecm problem that could cause what you are describing.
The only other thing that pops to mind that someone else mentioned is the motor mounts.
If you have a bad drivers side motor mount the torque will make the engine rotate and that will pull on the throttle cable.
Back in the old days before they started using clamshell type mounts.
If you broke a motor mount the engine would torque over and pull the throttle wide open and it would pull the gas pedal right from beneath your foot and slam it on the firewall.
Im pretty sure im not the only old guy who went on a couple of those **** your diapers rides.
In about 72 or 73 or so that was the biggest vehicle recall in history.
But all of those cars were already parked in the back yard becuase of the gas pannick
Our parents did not have the recall repair done those cars.
Us 80s kids had to find out about motor either buy running our selves over with the car.
Yep, he did do that.
Or by running the car through the bank lobby.
Yep, I did that.
Whatever you buy, it always needs new motor mounts and transmission mounts.
Kind of a personal rant but I have dealt with so many people who are chasing front end problems and shocks and the trying to chase down a thump.
And there is no bit of rubber left in the motor mount.
It might not be your problem but you need them anyway.

 

[PlatonicSolid]

That is a mechanical issue somewhere between the pedal and the throttle plates in the tbi and this also applies to carbs just in general.
That linkage may work just fine when you move it by hand.
Because you cant really feel if it is binding or not.
When it is running atmospheric pressure and vacuum are the forces involved.
And heat.
I think you have a binding throttle shaft or sticking throttle plates in the bore.
The allowable slop on the throttle shaft is pretty much zero.
You have a mechanical throttle linkage problem somewhere.
I dont know of any ecm problem that could cause what you are describing.
The only other thing that pops to mind that someone else mentioned is the motor mounts.
If you have a bad drivers side motor mount the torque will make the engine rotate and that will pull on the throttle cable.
Back in the old days before they started using clamshell type mounts.
If you broke a motor mount the engine would torque over and pull the throttle wide open and it would pull the gas pedal right from beneath your foot and slam it on the firewall.
Im pretty sure im not the only old guy who went on a couple of those **** your diapers rides.
In about 72 or 73 or so that was the biggest vehicle recall in history.
But all of those cars were already parked in the back yard becuase of the gas pannick
Our parents did not have the recall repair done those cars.
Us 80s kids had to find out about motor either buy running our selves over with the car.
Yep, he did do that.
Or by running the car through the bank lobby.
Yep, I did that.
Whatever you buy, it always needs new motor mounts and transmission mounts.
Kind of a personal rant but I have dealt with so many people who are chasing front end problems and shocks and the trying to chase down a thump.
And there is no bit of rubber left in the motor mount.
It might not be your problem but you need them anyway.

Original post throttle issue is a year old and solved by replacing throttle cable.
Motor mounts were replaced in 2007 when the engine was installed.

 

[PlatonicSolid]

Yeah those are pretty crusty but I've been able to get them off without breaking the studs. Fortunately the studs increase in dia. above the nuts.
This job is going to require a torch to heat those nuts red hot then carefully apply gradually increased torque till the nuts break loose. Stop and let cool a little until PB Blaser doesn't just smoke off when you spray it on there. Let it soak in then wet it again. You will probably have to work the nuts off by backing them out until they start to bind,re-wet,run them back on and repeat until you have worked them off. Bad thing is it looks the threads below the nut are almost gone. Hopefully you still have enough threads where the nut sits to hold it all together when you re-assemble. NAPA used to sell stud kits with the studs,springs and nuts. I recommend at least using the nuts and springs. I think your springs are toast too. To replace the studs you will have to heat the ears on the manifold red hot and repeat the process for removing the nuts.
Getting those nuts off will REQUIRE a six point,deepwell socket.

These flanges are not easy to get to. I think it's time to pay someone else to deal with this.

 

[someotherguy]

These flanges are not easy to get to. I think it's time to pay someone else to deal with this.

It'*****-or-miss. (edit 2nd time JFC it is HIT OR MISS) Sometimes I've got the ugliest flange nuts loose with just a 1/2" drive deep socket and long handle ratchet. Other times went after them with the 1/2" impact. Sometimes they just give up and spin off, other times they give up and break off.. then it's time to pull the manifolds and determine whether to repair, or replace. Both of the manifolds on my '93 7.4 are cracked, so that's an easy decision.

Richard

 

[Scooterwrench]

These flanges are not easy to get to. I think it's time to pay someone else to deal with this.

Then there's that option.

 

[Schurkey]

These flanges are not easy to get to. I think it's time to pay someone else to deal with this.

For what it'll cost to "pay someone else to deal with it", you could probably buy two new cheap-junk Dorman manifolds, (or "good used" manifolds, IF such a thing exists.) Then it doesn't matter if the studs break.

Might have some trouble if the manifold-to-head bolts break, though.

Any way you look at it...exhaust work and plumbing stinks.