Hey right now I have an 99 1.8T and its giving me about 15 mpg, and I cannot figure out why. I ran fuels system cleaner and changed the air filter but it only gave abou 1 mpg more. Anyway I'm reading to the post and I figured I will just replace everything. the car has about 114,000 miles on it and I don't know when the owner before had stuff changed. I just got it at 110,000. The only thing I know is that he got the timing belt changed at 103,000. Anyway here is a list of things I want to change in that order.

Spark Plugs
O2 Sesnsor
MAF Sensor
Fuel Filter
Diverter Valve
Hoses if Neccessary.

I will run it through the VAG COM when ever I get a chance but that seems like the plan. Let me know what you guys think. Also how much do you think these parts will cost?

HeCareth

 

Not a bad plan. Have you had it looked at yet?

You're gonna spend a mint on those sensors..try to get them used.

-T

 

ecstuning would probably be a good place to check for all those parts...looks like a pretty good list to me...bad O2 sensors can kill your gas mileage, i'd say do that first...i can't see old spark plugs causing that much of a drop, but it's probably a good idea to change those anyway...none of that stuff looks super expensive, except maybe the maf sensor, i think for some years they are pretty expensive

 

yea change the plugs, then my next guess woul be the cat. do u ever smell any kind of fumes.

 

No I smell no fumes, but sometimes the engines revs too much, say when going up a hill or when I start to move again from a rolling stop, and sometimes it acts normal. I figured all this could be related to gas mileage. I have no clue though.

 

that sounds more like a sensor problem if it's intermittent

 

MAF or o2 sensors is my geuss