P0161 - Heated HO2S sensor heater circuit, can be either a bad sensor or missing power supply.
P0300 - Random cylinder misfiring detected. Possibly related to P0120 and P1120.
P0450 - EVAP pressure sensor sensor malfunctioning.
P1120 - Accelerator Position sensor ciruit malfunction.
P0120 and P1200 are the main problems you need to address before you go to others. Both are critical for engine performane and idle controls.
These problems were not mentioned in earler post so I guess they were a result of you working on the vehicle. Recheck the wiring connections and ensure they are clean and secure. Ensure connectors are correctly plugged in and you would need to perform diagnostics if you can't find any faults, which would be easier if you have a scan tool.
Friday, September 14th, 2012 AT 11:22 AM