I replaced the head gasket on my 2005 sentra and now I can not keep the mil (check engine) light off. I am getting code number P0011 and I can clear the code but the light will come back on some times within 30 minutes some time a day later. I have retimed the the cam shafts to crankshaft many time, no problems there. I have replace both the intake cam advance solenoid and intake cam postion sensor, changed the oil. Dose anyone have any Suggestions.