I have a 2010 Aveo 1.6L Ecotec that will run rough and stall on start up, only if it has sat for a few days. If you give it some throttle is clears up within 5-15 seconds and will run completely fine. No CEL. The car only has ~50K miles and the customer purchased it from a elderly relative(probably sat unused for a long time).
LTFT is -3 at idle which made me think leaking injector. I performed a injector leak down test and it passed. I even did a injector balance test and all were within 1psi. Fuel pressure is within spec.
My next thought was leaking purge valve, but fuel trims did not change with the canister line removed from the purge valve. I confirmed there was no vacuum leak through the purge valve when not energized.
MAF, MAP, ECT, IAT readings appear normal. I cleaned the throttle body, with no change.
Next I shifted focus to the VVT system. Both VVT solenoids ohm out to 7.8 ohms. I'm seeing short occasional cam variance of 2-4 degrees. But mostly there is zero variance. My scan tool has an actuator test for the intake actuation and exhaust actuation. The intake test seems to work fine. When I enter the exhaust actuation test, most of the time the engine dies before the data PIDS even populate. I swapped the VVT solenoids between exhaust and intake with no change. The car still dies most time when entering the exhaust actuation test. When it doesn't die, it works fine and I'm able to command 5, 10, 15, and 20 degrees of actuation, without variance. This makes me suspect a sticking exhaust cam phaser.
There are DTCs in the Vehicle Comm. Interface Module:
B1000-31
B1000-3C
B1446-12
B1447-04
I'm not sure if these are related to the issue or not. Not much info available on these codes.
If anyone has insight, please let me know.