[MatthewH]

Thanks to both of you for spending some time looking at the logs.

The MAF sensor was my first thought when I first bought the car 12 months ago. There was no MAF specific codes but I replaced it as a precaution as it looked original. The first one I fitted was a new genuine Audi part (although bought on eBay from someone who never fitted it - it was still boxed and looked genuine). This didn't make any difference. A few months ago I purchased a new Bosch MAF in case the previous one I purchased was dodgy (this time brand new from Amazon - not a third party seller. All seems genuine and I verified the serial number on the Bosch website). Still made no difference unfortunately so I think I can rule out the MAF sensor itself.

I'd say the car seems to pull fine up to the limiter. I also have a 300BHP Mondeo and the A8 certainly feels a bit more powerful, despite the quattro and automatic gearbox power losses.

If anything, I'd say it struggles at low RPM (<2000). If driving at a steady 30mph and go to accelerate, the engine labours a bit for a second before dropping a gear. This is my first automatic car so I'm not sure if this is to be expected - I assume in "D" mode it tries to keep the car in the highest gear possible. This isn't as bad when driving in "S" mode as the revs are held higher.

I'm pretty sure there are no leaks from the intake manifold. When I had it off last week, I went over every vacuum hose and PCV breather and they all seem good. Throttle body gasket and intake manifold gaskets were replaced. Only area I've not checked is the brake booster - I believe the brake booster pressure can be checked with VCDS so I'll look into that.

I've also checked for leaks with brake cleaner and propane around the manifold and injector o-rings but none found. The car has done 150k miles and when I recently replaced the fuel filter it was pretty clogged.

I noticed on my logs there was some timing retardation (up to 12) at high RPM. Is this normal? This is not an area I'm too familiar with.

I'll try the tests you mentioned tonight (unplug MAF and also simulate rich condition).

I'm in the Bolton area so not too far away.

ainarssems: Thanks for the chart. You're right in saying there is no obvious pattern to this behaviour and also no fault codes other than "too lean". The only symptom seems to be the MPG!

Thanks