Gau8mechanic
Registered
My '97 LSC likes to stall once in awhile. Happened twice going down a hill - both times decelerating to parking lot speeds. Happened twice backing up - both times backing into my driveway. Doesn't stumble or shudder. Just turns off. Restarts fine. The instructor I have in my auto tech school has an Autel Scantool. He hooked it up and we looked at my long and short term fuel trims. LTFT on passenger side is dead on zero. LTFT on driver side is 5.85%. We thought vacuum leak. Sprayed carb n choke cleaner around the back side of the intake and it immediately reacted and dropped to -12%ish. Started to stumble as the computer tried to readjust trims. We repeated this twice. Used a smoke machine too but smoke only came from the intake airbox. None from anywhere on the engine. We suspect the upper and lower plenum gaskets. Does anyone have some insight on this that could help me better assess this?