I just recently had a full tune up, changed the water pump and timing belt. I am still getting only 17mi per gallon. I was told I should be getting at least 23mi per gallon. I even put a Techron treatment in and still no better.

 

check to see if your fuel pressure regulator was unhooked on accident. also the timing may be off

 

I just got the timing done how could you tell if the timing is off. Are there any detectable signs. Could bad gas mileage be caused by a bad O2 sensor. I was told my TPS was bad due to the constant reving while its not in gear.