Your MPG will probably be down because you have removed the air feed cover from your air filter, it will be pulling in heat from the engine bay.
It's been refitted Rich and MPG is still poor.
Fitted some spring islolaters on my front springs, after fitting the Eibachs i started getting a slight rattle on uneven road surfaces. Contacted Eibach who supplied the isolater free of charge. The rattle has now gone!
Also another friend who has an 08 Leon 2.0 tdi 170 had his car towed to a garage today following a slight misfire then engine cut out. It's been diagnosed as an inlet manifold failure resulting in damage to a piston, valves and possible turbo. That's two now that i know of with failed engines due to the manifold!
Thats not good! Might have to get mine checked out.
On a better note, the cars booked in for DPF delete on Wednesday with Big Fish.