tire inflation is critical as well! I went one tank of gas with under inflated tires on my 94 Metro, the result was 6mpg - it was low by about 8psi or so, everything else was my typical driving, timing on the engine is critical also - I did an engine swap out not to long ago, it run fine (so I thought) for about 3 tanks of gas and the MPGs were in the mid to high 30's. I set the timing correctly and now I am currently getting and average of about 44mpg. It's funny to see how much little things do effect the MPG.