High idle, hard start, etc

[gretchenthe454]

Hi everyone! This is my first post here. A couple months ago, I bought a 1992 sierra 2500. It has the 454 with the nv4500 trans. PO had both rebuilt within the last 10,000ish miles. Since taking ownership, I've done small fixes here and there that's to be expected on a 30+ year old truck.

So here's what's been going on... a couple days ago, I noticed that the truck hesitates and acts like it's going to stall when starting out in each gear (and it has stalled on me while driving and in motion.)
The truck will start just fine when cold but when warmed up, I have to put the go pedal to the floor while turning the key to get it to start.
And lastly, when coasting, not in gear, the truck sits at 2k rpm.
I just replaced the fuel pump assembly with no changes in performance. Anyone have a clue as to what the problem could be? The fuel pressure regulator is what I'm thinking now but would like some thoughts before I go tearing into the engine. I'm somewhat mechanically inclined but unfamiliar with these engines as this is my first obs (if there's a few YouTube videos on the subject, I'm confident I can get it done)

Thanks in advance to anyone with some pointers. Happy to be a part of the forum!

 

[Jroctizzle]

Vacuum leak may be the cause of the high idle, (when things rattle around from driving it may be shaking something loose) I tracked down one I had recently and it turned out to be the oil catch can I had put on a couple years ago (my idle was sitting around 1400).
Good way to check if you have one is to take the filter off and plug the IAC port, (back left of the throttle body) truck should stall, not even start or barely run at all when it’s plugged.

If the vacuum lines are good I’d look at the injector spray pattern they could be malfunctioning or clogged.
My truck did the same, almost stalling out and then jumping when I would hit the gas when I first got it, ended up replacing the fuel pump, filter and injectors and deleting my egr.

if the egr is still connected it may also be stuck open so it’s feeding the engine exhaust fumes when it shouldn’t be, not sure how much it would influence the dips and stalls but I got rid of mine and haven’t had issues since.

Lastly maybe check your base timing, if it’s off it may be messing with the electronic timing advance in the computer so it thinks it needs to do things it doesn’t.

Also posting a picture from another thread on resetting the IAC valve.