2005 A8 D3 4.2 (BFM) - Low MPG

[MatthewH]

Thanks Lee. Yes, I thought it may have been a problem that occurs under load only - I just thought bad cam timing would cause rough idle (and bad emissions) so I was hoping that was not the case! It's still worth checking as you mentioned. I'll get a photo of the timing-related VCDS values you mentioned later on today.

People have also mentioned the hydraulic camshaft adjuster valves as these can be a common problem on this engine - I think the plastic "shoes" wear down and cause the chain to become loose. This uses causes a loud rattle though which I don't have.

I actually have a spare fuel rail with injectors so I'll probably start with these. I was planning to rebuild the injectors with new seals and microfilters. I tried to remove my injectors when I had the intake manifold off but the fuel rail wouldn't lift off (with only the injectors holding it in place). It felt like I was going to bend the rail if I pulled any harder so I ended up leaving it attached.