I'm on here checking out some info for my brother. He recently bought a 318is auto coupe for work useage (not wanting to run his truck into the ground or pay for the 23/24mpg fuel usage).

Checking out the stats online it seemed most people were getting 30mpg-ish, maybe more on a run, but he is returning no more than 23.5 on a normal country lane trip too an from work. I get that much from my celica 2ltr turbo 4x4 japmobile booting it everywhere- surely something is wrong somewhere?

Is there anything i should start with? In my car I'd go straight for the air filter, then o2 sensor - but in a beemer I'd not know what was most likely to cause problems. Is there a diagnostics facility I can do at home, or will I have to test the sensor manually (get it hot, check rate of change of voltage etc)??

Any help appreciated, im pretty experienced but with it not being my car and only meeting him once every few months I want to go armed with things to look for :)

Cheers all