454 Sticky Throttle is a death trap

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

Coulbe wore throttle shaft bore, dirty intake bores on the tbi, or sticky throttle cable.

yevgenievich said:

Coulbe wore throttle shaft bore, dirty intake bores on the tbi, or sticky throttle cable.

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I thought the same thing, but since throttle moves smoothly with engine off, I believe this is less likely.

That idle TPS voltage doesn't seem right. @PlayingWithTBI can you confirm what it should be?

618 Syndicate said:

That idle TPS voltage doesn't seem right. @PlayingWithTBI can you confirm what it should be?

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.60 volts +- .08 volts at idle.

I thought it's supposed to be lower too. Mine is set .48-.50v

What about bad engine mounts letting it shift when placed in gear putting throttle and cable in a bind?

Check for any vacume leaks? They are known to cause high idle problems.

Dropped88 said:

I thought it's supposed to be lower too. Mine is set .48-.50v

Click to expand...

TPS Brand: SMP, Model: TH39, Instructions that came with it state 0.60 - 0.64 V

618 Syndicate said:

That idle TPS voltage doesn't seem right. @PlayingWithTBI can you confirm what it should be?

Click to expand...

I like it a little lower but, it's more important to get the full range from ~.58 at idle and go smoothly to ~4.5+ at WOT. This attachment says .58 - .59.

I agree, your throttle shaft may be getting into a bind when the engine is running due to the vacuum sucking it into a worn slot or something like that. Try wiggling it up and down, in and out. There are boring and sleeving kits out there. I think @tayto does it too (for a nominal fee, ha ha)