I've owned my 02 tdi for close to a year now and I'm discovering that my average of 40-45 mpg is, in fact, quite measily. In my searching through the forum i came across several different people mentioning venting. What is this? Also is there some kind of additive that can help increase by mileage? I had one random tank of fuel that got me 50mpg (638 miles) on the dot but since then have never repeated that. Egr is deleted and has an aftermarket turbo which is still the oem size.