Hi like i said i got an 08 Acadia that is acting up. i just bought it. It starts easy and idles fine for a few minutes, then starts misfiring and the service stabillitrac light on the dash comes on. it throws code p0300 random misfire. and p0174 lean system bank 2. checked for vacuum leaks, changed oil, and filter, air filter, mass airflow sensor, torque tube, and spark plugs. did not fix issue. please help.