2003 Nissan Altima service code p0011?

"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)

symptoms
Hard starting, bad idle and possibly stalling issues

caused by
Incorrect camshaft timing
Wiring issues (harness/wiring) in intake timing control valve control solenoid system
Steady oil flow to VCT piston chamber
Faulty timing valve control solenoid (stuck open)

the fix
This code indicated a mechanical issue, electrical troubleshooting wont help so replacement of the VCT or one of it's related components is necessary.