So i have a 94 obs chevy with 1999 lq4 and 4l80e. Truck runs great but has developed an issue where it dies a few mins after being put in gear and once you start driving its a little sluggish from a stop but then fine. Only other issues it has is the low voltage for knock sensors, and when coming to a stop the down shifts from the 4l80e are hard.

I have tried the following to fix the problem.
Switched IAC sensor
cleaned maf
Cleaned TB
Replaced plugs and wires
New fuel pressure regulator
new stock injectors

torque app info
14 volts
19inchs of vacuum
Timing does jump around 14 to 28 degrees
Afr is 15 to 1 at idle

Stock setup expect cai, and tune to get it running.

 

Could be the MAF and/or MAP outputting erroneous data, while the ECM is not flagging it.
My 2003 Silverado with a 4.8, DBW, and manual trans would die at a stop sign. I replaced
the MAF and MAP, which fixed the problem. I replaced both at the same time, so did not
isolate which one was bad.

 

So after more testing, the truck will idle in 1st/d but not with the shifter in overdrive or reverse. Also after coming to a stop and trying to accelerate there is a harsh shift, like the trans never fully shifts down to first gear.

 

Is the lockup clutch releasing?