Could it possibly be clogged fuel injectors? Have you run a fuel system cleaner through the car yet?

 

im not sure i get what you meant. how can i do that?

 

He means a fuel-injector cleaner (solvent)that you pour into the gas tank. Chevron Techron, or several other brands here in USA. I don't know what's available over in Latvia.

 

Or something like seafoam. You pour it in the throttle body throat, the gas tank, and oil crank case.
Here's a link: http://www.seafoamsales.com/motorTuneUpTechGas.htm

 

miks, i dont know how much you will be able to improve it.... Was it you that said your car was 150hp? If it is that means your car is just dumping more fuel into it in general after all it doesnt have vtec for the whole gas economy, granted yeah it shouldnt be as bad as 13mpg but it is in city with a more agressive cam so I can understand why it would be that bad, Have you driven a full tank highway at about 120kph?

 

yea my car is 150hp non-vtec, but its mileage should be ~18-19MPG in city (one friend has the same engine on wagon chasis).
mileage is bad also on highway 23MPG at 60mph cruising (it should be more like 28-30).
ill try that cleaner.
although i already emailed the dealer for a full engine diagnostic posibilities.

how about all those air meters, o2 sensors and lambda zondes?

 

Well, if thats what all the information says your mpg/kpl should be then ignore what i said, as for the o2 sensors, those being defective could cause that drop, but those are also not cheap and you should resort to replacing those when youre absolutely sure they are bad.

 

i checked the repair manual for O2 sensor response monitoring. ill do that when ill be able to get under the car for connection.
i already checked the cost of it, ~150$ at dealer, 50-100$ on ebay. pritty high pay for such a little ****