The codes are now pointing to a problem with Lambda sensor 1 - heater circuit and range / performance.

Can you measure the resistance of the heater? (between the 2 white wires on the sensor, normally).

Kevin

At last , problem fixed!
Investigating #1 lambda sensor ( which I replaced last October) Took it out and what!! , there were little bits of broken ceramic inside it just too large to fall out of the perforations in it. Put in a OEm lambda sensor.... and all problems went away immediatly. The OEM sensor head is very different and not as open.

So now perfect acceleration, hot or cold, No MIL light.

Rule 1 not to be broken - Only fit OEM parts , after market parts - they may screw in the hole and plug in but if they don't function properly you end up buying again anyway and wasting a lot of time!

Thanks for the suggestions everyone , a great help.

After sorting this I decided to replace the cam sensor anyway as I had already bought it.
I learnt one hell of a lot about OBD 2 while doing this and am going to get a plug in that allows live readings to be taken on a laptop. I also found for the first time a list of everything that can bring on the MIL light (EML) and the cycles the GM uses in the ECU to assess if the emissions systems are working properly or actually tested. I'm used to complex systems but I have to say the ECU is doing a lot more than you might expect in clocking in faults, holding them as pending and counting until it resets tham ( if at all) without this information no wonder its confusing dealing with one light and a limited view from a few fault codes.

Now on to the rattling exhaust, the minor paint jobs where some moron hit and run in a 3663 lorry and an MOT!
Vince

Excellent. Glad it's sorted.