Just because the car is not as quick as the TDi, it is not reason to be looking for clogs. Compare 0-60 times with literature, and try all the other tricks first.
There area couple of advantages that your TDi will have over the benz. One is weight, the other is gearing. The jetta is significantly lighter than any S-class benz, and the gearing is so short on a TDi that it is hardly in first or second. With the benz, it usually starts in second gear and lasts until 30 or 40 mph. (Those little dots you may have noticed on the speedometer are actually redline shiftpoints.)
There are also a couple of tricks that can be done to make the transmission always start off in first. I personally choose not to do anything permanent (ish) like a parallel kickdown switch. This basically makes sure that the transmission thinks the car is always floored and can burn out the kick-down solenoid. The easier, more reliable way is to just downshift and stomp on it. On my '93 diesel, I have the bowden cable, which modulates the shift points, a little tighter than most would like.
As for the fuel mix if an intercooler were installed, that would involve the ALDA thing that I described. Its purpose is to adjust fuel mix for the atmospheric pressure, as it can vary by altitude or boost. This is not something that should be messed with under normal circumstance, so I decided not to mention it previously. Turning the screw on top couter clockwise will give a richer mix. The manual suggests only 1/4 turns, since it is that sensitive. It is also a real PITA, as mine is running rich (still) since I last played with it.
Yes, the 928 is an S4, the first year of the S4 actually.
\'87 Mer-B 300D (220,000 miles) (sold)
\'93 Mer-B 300D (173,000 miles) (sold)
\'87 Porsche 928 (101,000 miles)
\'98 Dodge Ram quad-cab (250,000 miles)
\'2001 CLK430 Cabrio (50,000 miles)
Past cars: 1969 mercedes 250, 1981 300D, 1972 220D