This is my very first post here so we'll see what happens lol. I bough an a4 1.8T quattro Automatic last April and I averaged about 22 mpg for most of the time. In November I had it in the shop for a new oil plan. Since then I have not gotten more than 18mpg on any tank of gas and have averaged about 16 mpg the lowest being 14 mpg on a full tank. When i first got it back from the dealer and took my first long drive it didn't quite feel right. At 55 MPH on the highway it feels like the car wants to down shift. Like the engine is laboring. Zero codes show up in VAG COM so I thought maybe i was just being paranoid. I changed the plugs, new air filter, new fuel filter, new coolant temp sensor, new MAF sensor and still felt the same. Didn't want to have to take it back to the dealer and complain because well, i haven't had the money. My last tank of gas was 16.3 mpg mostly highway driving and I just can't figure this out. I don't drive fast, I don't accelerate hard I'm pretty easy on my vehicles. Anyone have any suggestions of what they might have messed up at the dealer changing the oil pan that would cause this or any ideas at all about getting better mileage. I have read on a few message boards of people getting 350 miles on a tank and I'm not getting any where near that. Any suggestions would really help. Currently I'm checking for any boost leaks. I did get one code in VAG COM just the other day

1 Fault Found:
17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!)
P1297 - 35-00 - -
Readiness: 0000 0000

I bought a new DV just waiting for it to arrive. Gas in the Pittsburgh area is heading upwards of 4 bucks a gallon and I'm hoping i can fix this I love the car and don't want to sell it. Thanks.

 

Gas just hit $3.69/gallon for regular here, so $3.89/gallon for 91 & 92 octane that our cars need. Ouch factor is very high and only getting higher on getting bad fuel economy, so I certainly feel your pain.

16 MPG for mostly highway driving is NASTY. I used to average 27+ when I had a long (27 miles one way), all highway commute, now with an 11 mile drive at lower % highway and some pretty long stoplights to sit through, I'm still averaging 23-25. I get downright despondent if I get less than 350 miles on a tank; with that longer commute I used to have, it was uncommon to get less than 410-420 miles on a tank of gas, and I'd occasionally eke out up to 440. ('02 1.8T Quattro 5-speed manual)

That fault code's description sure sounds like a boost leak. Seems like you're on top of it. Good luck, and let us know what the resolution is; that way others who search for that fault code in the future will have something to go on.

 

a vaccume leak will cause the system to readjust mixtures. I would hope that ur replacing ur dv fixes it but if not i would do a search through ur vac system to make sure u dont have any other leaks

 

Is that fault code making your check engine light go on? If so , correct that problem & see what your milage does.