Engine stumbles but only in drive

[rebel04343]

Ok well this is a new one for me. I have a 2000 k2500 crew cab sb. Small block 350 engine. Truck runs awesome but sometimes when I’m in drive and sitting still the truck with lug down to just above stalling then over compensate and rev up slightly. It won’t go till the point of dying. When you throw it in neutral problem clears right up. Something with transmission? Anyone here has this issue? Looking for the fix. Thanks for the help!

 

[Nad_Yvalhosert]

Is the A/C on and cycling when it happens?

 

[rebel04343]

No unfortunately it hasn’t been warm enough in goofy Ohio yet lol!

 

[Nad_Yvalhosert]

My initial thought was the idle-up feature when the compressor cycles, combined with clogged IAC passages.
You're gonna have to datalog this while this is happening.

 

[rebel04343]

I’ll check out the IAC valve. Maybe it needs cleaning. Just weird it only happens in drive.

 

[thinger2]

Highly unlikely for it to be a transmission problem.
More likely an emissions component or a vacuum leak or an ignition system problem.
Even a sloppy timing chain but I doubt that.
A worn out distributor can also cause that.
If you dont get a check engine light,
And you have cleaned all the crusty wires and grounds.
And you dont just have a bad plug or plug wire
Then it is time for some live data.
Clean up all of the electrical connections first.
All of them front to back.
If you look through this forum you will find countless cases of people who have replaced every bolt on component and swapped transmissions and they still have the same problem.
If it aint rod knocking and valve broken zero compression jacked up.
If the timing chain hasnt skipped.
If you dont have a bent pushrod or a collapased lifter or a bad cam lobe or a burnt or stuck valve and all of the other normal Kerfucked mechanical issues
Its an electrical problem or a vacuum problem or a timing problem or a fuel problem.
The only real difference between a TBI and a Quadrajet is that any dope can randomly turn screws on on a Q-jet and make it pop and fart and flood.
And claim to be a "carb tuner"
TBI does not let you do that.
GM TBI is a gatekeeping system that will stop a screw turning monkey in his tracks.

 

[LC2NLS6]

Over the years, on TBI gm trucks I've learned to check fuel pressure first. Then verify timing. Then start pulling codes.

 

[PlayingWithTBI]

We're talking about a 2000 truck. He should have a Vortec engine shouldn't he? I'd still check fuel pressure and then data log to see what's going on when it lugs down.

 

[rebel04343]

We're talking about a 2000 truck. He should have a Vortec engine shouldn't he? I'd still check fuel pressure and then data log to see what's going on when it lugs down.

Yep it’s a vortec I’ll start with fuel pressure.

 

[Schurkey]

I'd start with a scan tool. If you have a fuel problem, it should show up in the fuel trims. If you have an IAC problem, you should be able to see it in the IAC counts, and the commanded idle speed vs. actual idle speed, etc.