err I may be wrong, but I own a 2007 Passo as well and the meter says between 15.5 to 16.3 avg mileage and i am travelling from Rawal Rd. to I-9 off and on (moderate traffic). current average keeps changing between 8 km/l to 50km/l. which seems about right because my avg travelling daily is around 50km and I put 1000-1200rs. petrol per week (5 days).
did u by any chance remove your cat converter? because if u did that will hurt the mileage. if not than get both O2 sensors cleaned. mine is not an excellent condition car 116k ODO (or atleast this is what it says, grey import readings are not reliable, I only had the car for past 1 yr). and I am using simple toyota oil filter, shell 10-40 (yellow), Lepon air filter, DENSO IKH20 or VKH20 plugs and vehicle is more or less stock conditions. my avg. driving speed on 9th avenue is also 80-90 so not really light foot, neither am i turning the ac on/off.
yes engine does vibrate when ac is on and i am stopped on a signal and keep the car in D. you should only worry if your plugs are getting oil fouling or oil level decreases before 5-6K single oil change. one thing that helps a bit with it is if you get a 18g simple dc cable and connect the engine body (tappet cover) with battery ground (but the difference is very small to notice under normal driving conditions)
