stock vs modified
I'm a newbie here too...picked up an 03 jetta wagon tdi Last august...had 92,000 on it (also in AWESOME condition)...coming up to 110,000 already! I'm just hammering the miles on the awesome car! I had GREAT plans to modify...nozzles, chip...and somewhere along the way I've totally fallen in love with the thing as is! I recently bought a custom made WESTACH dual Exhaust Gas Temp/Turbo Boost gauge on a TDI club group buy...and I doubt I'll install it now...prob sell it (it's an amazing gauge...not sure I WANT to sell it!) I get GREAT mileage as is, and getting better all the time as I drive smarter! One thing I would recommend is getting a ScanGauge II..it hooks up to your OBD II port. What an amazing little piece of equip that is...it gives you real time monitoring of a bunch of things...in gauge mode I have 4 displays up at the same time...MPH, MPG, Intake air temp and coolant temp...but you have many more to choose from. Then in Trip mode, it gives you MPG of the tank, miles driven, miles left on the tank..all that useful info. (AND, it also will read/clear any engine codes you should happen to get!) I'm continually getting over 700 miles on a tank now...averaging around 47mpg overall. I get a rock solid 52 on the highway at 65mph, and around 42 to 45 city/combined (driving to/from work). If your car hasnt' had it done yet, search for and do the VENTECTOMY on your fuel tank filler neck...simple to do, and it lets you use the ENTIRE fuel tank! (when I first filled the 'empty' tank it only took like 13.5 gallons...I was wondering what the deal was...as it really kills your overall range on a tank).
So anyway...welcome to the TDI world....and good luck! I LOVE this site...so much info, it's a total overload (in a good way!) Talk about a 'do it yourself-er' paradise!