drop in mpg

[ajw1971]

Hi all, new to the forum so have been having a good read of your posts, some informative stuff. So it would appear that there are many and varied faults and problems with the trustie Passat.

Well, mine is as follows (they may be linked in some way or another)

Model, 2008 2.0, 170bhp, TDi SEL saloon, 146,000 miles.

Like a few other posts, had a bad smell from the exhaust, engine would cough with giving it the beans from about 4000rpm. Changed the fuel filter and this seemed to help with the coughing. bad smell from exhaust still there. When driving at say 30 - 40mph, using light foot on the throttle, the car would feel like it does with the cruise control on going down hill (ie, as if the throttle was switching off, and on quite quickly) Normal acceleration was fine, you couldn't notice it. Fuel consumption was good though achieving 50+ on country A roads, and 70-75 mph motorway journeys. It was like this for many months before i got really fed up and tried to do something about it.

Decided to try an engine carbon clean (Not terraclean) this uses a small amount of hydrogen to burn off carbon deposits in the intake and combustion system (or so i'm told) This has helped quite a bit, the engine is a bit quieter, on/off of the throttle appears to have gone and so has the bad smell from the exhaust. The guy who did it plugged in the VCDS and it should the EGR valve was barely opening before, but is much better now. Turbo is spooling up easily and all seems good. He said the fuel economy would drop initially but should recover and probably marginally better than before.

Now here's the problem, i had this done a month ago, and over the last 2-3 weeks the economy is worse than before, just about getting 46-48mpg. With driving like Miss Daisey and the occasional coasting to a roundabout it may just touch 50, but this is rare now.

Now it does need a service so i'm going to get this done this week, ie new oil and filter, new air and fuel filters. It has just had 4 new tyres fitted and new rear brake pads. The front discs and pads were done about 2 months ago.

Would it be something as simple as it just needing a service or could it be something more sinister. The car is good, i like it, but it's starting to get on my nerves now.

Sorry for the long post but thanks for your time in reading.