Righto, I have 11years experience with these. It could be two things wrong. One fix is considerably cheaper than the other.
The code that you want to be looking at is the P0430. This code will appear if there are.....
1. leaks in the exhaust system, vacuum leaks in the intake and/or the Evap emissions purge system.
2. The Catalytic Converter is farked.
To test the evap purge solenoid,
Unplug the hose AND connector going to the purge solenoid (you will need to unplug the hose off the valve that comes from the firewall NOT the end that goes to the intake manifold) and with the engine running, put your finger over the end of the valve where you unclipped the hose from. Leave your finger there for about 30 seconds. If you feel the valve sucking your finger to the end of it, IT IS LEAKING and needs to be replaced.
I will garantee that your evap purge soleniod valve WILL be leaking/bypassing "extra" unwanted air into the intake.
Replace this first then clear all codes and drive a considerable distance
It will take two Ignition cycles before the ECM parameters will look for and pass these DTC's.
Try this first or you may be replacing your cat converters for nothing.
I have taken it to local auto shop to get the things you mentioned above checked out.
he checked out exhaust for leaks, that’s ok
inasked him to do check vacuume etc, he said purge value is good and only way to check rest is with a smoke machine...??
he took it for a run and said runs nice, no misfire.
the interesting thing is this.... he replaced cats in 2014 with aftermarket ones because no one could get to bottom of this issue, he said cats are fine, only done 30000k on replacement cats.
so I’m no better off, there is nooone in the district with DyNo tune who will touch Holden, so I guess it’s off to the Holden dealer to see if they can diagnose the issue.
im losing faith in any mechanics at the moment.
his words were it’s got a gremlin in it,
the frustration is the car runs great, fuel economy is great, it’s just the light I want gone,,!!!!!!!