OXY sensor will play a role in this as well as
AFM settings being too rich. meaning you should lean out the air/fuel mix
TO CHECK AND ADJUST MIXTURE:
1. start and run the engine until its at operating temperature
2. set idle speed and timing to specified values
3. take off the passenger kick panel to view the LED's on the ECU
4. start and run the motor at 2000rpm for 2 mins
5. check the flashes from the LED's on the ecu while at 2000rpm, they should both flash together more than 5 times every 10 seconds. if they don't you have ecu or oxygen sensor issues (refer to the picture at the bottom explaining the interpretation of flashes other than what are stated)
6. if there are more than 5 flashes per 10 secs, stop the engine, disconnect the wiring connector from the AAC valve and the throttle switch
7. start and run the engine at 2000rpm for 2 mins
8. let the engine idle
9. the leds should now flash simultaneously
10. if the green light is flashing more the mixture is lean, if the red is flashing more the mixture is richer than it should be.
10. if the LED's do not flash together remove the plug next to the Air flow meter connector and adjust the screw until they flash together (clockwise raises the resistance and leans the mixture, anti clockwise lowers the resistance and richens the mixture)
11. replace the plug, replace the AAC and throttle switch connectors and return to instruction 4. do the test again to check that the mixture is now right
12. if the mixture cannot be adjusted so that the leds flash together
for further info on getting the l running right click
http://forums.justcommodores.com.au...ne-troubleshooting-maintenance-step-step.html