Hi There,
I've had a look at the inlet manifold. Took the back pipe off the engine and fed a usb camera inside. Tried working the linkage and the flaps move and seem ok. I've also popped the vac pod and linkage off and cleaned those as per
http://forums.quattroworld.com/a8/msgs/44689.phtml and that all seems fine. I did also take the top half off my old dead FL D2 S8 to have a look at the workings, though I understand that the 4.2 D3 A8 is a more basic manifold.
Also had her Carbon Cleaned which she idles a bit nicer and is smoother and maybe a little more responsive, but made no difference to the LPG fault - I made sure they flowed the gas through both bits of the inlet manifold too!
At which point I can't see anything wrong with the inlet, though without popping the top (and getting sealant issues as I don't think you can get a gasket) I can't be 100% sure!
I've VCDS & OBDEleven and the Zenit Pro LPG software so diag kit should be fine!
I've swapped LPG injectors and the fault stays with Cylinder 8
Running on Petrol, I ocasionally get 16804+16814 - Cat system bank 1 & 2 efficiency below threshold - I've checked the sensors via VCDS aging test and they come up below 1 and pass, though I find it odd that it's both Cat Banks at the same time!
I typically get 16684 (random) & 16692 Cylinder 8 on LPG....However the other day I also got 17718 Cylinder 10 short to ground ???
LPG needs to be warm, so you can't/shouldn't start on LPG. I can do it from warm and clear codes and you get a flashing Engine warning light. Sometimes the EPC light too. It's almost imediate.....A minute or two later you get the system erroring and cylinder 8 gets disabled, though LPG will still run on 7 cylinders.
I've noticed that high reving seems to make it a bit better, but still errors!
Lee