Mechanical Injection Timing adjust:
1) Buy VCDS:
http://www.ross-tech.com/ YOU CAN NOT DO THIS ADJUSTMENT WITHOUT IT.
2) Get car fully warm, like a 30+ minute drive. You need coolant and fuel at full operating temps.
3) Connect VCDS cable. Fire up VCDS. Load up the TDI Timing graph checker, see this page:
http://www.ross-tech.com/vag-scope/TDIGraph.html
MAKE SURE YOU PICK THE CORRECT GRAPH FOR YOUR CAR -> lower right drop-down box.
If timing is incorrect,
4) Turn off car. Pop hood. Remove timing belt cover.
5) On the pulley for the injection pump are three small bolts and the large center one. Use appropriate socket (1/2" worked for me) to loosen the three bolts JUST ENOUGH to remove tension, do not make them very loose!
6) Use 22mm socket to adjust the center nut. Toward back of car is 'retard' , toward front of car is 'advance'. You need to use TINY TINY TINY adjustments. The entire 0-255 range is LESS THAN 1mm. Don't turn the bolt, tap the wrench very slightly, while applying pressure.
7) Tighten three bolts up.
8) Turn on car. Fire up VCDS and check timing.
9) Repeat #5-#9 at least four times, because you'll adjust it too far in one direction or the other.
Took me at least 10 times to get mine just right.