Coincidentally I've changed mine (PD 170 BMN) yesterday to see if it helps cold starts. It's that time of year, when the temperature drops below 10degrees these engines don't like to start smoothly. I've had two PD170s and both did the same thing when the temp drops below 10/12degrees is so. It's not even that cold to trouble glow plugs, but something affects it. Once it's run it will fire up perfectly all day, just that overnight and the next morning it's rougher than normal.
It's only recently I read about the torsion value. I measured mine at +3.6, so thought I've found the problem! I have adjusted it to 0.0 on the inlet cam vernier. So far this morning (not particularly cold in Manchester this morning, around 12degrees), it still didn't start smoothly so I don't think the torsion value is the answer. Also of note is a noticeable drop in power, the engine runs very smoothly however, but has a noticeable lack of punch.
Curiously, I had a remap a couple of years ago but took it back and had the smoke map uplifted across the board to try and see if it helped response and power (it didn't, but I'm positive the cold starts over that winter were fine). As the car was smoking a little bit more than I liked when warm I took it back to the tuner (Unicorn who was extremely helpful) after about 4 months who lowered the smoke limit back to what it was and I'm sure the rougher cold starts returned (just like the stock engine I might add, no criticism of Unicorn at all). It's definitely a PD170 curiosity, and I reckon some kind of cold start fuelling adjustment would help.
If you have VCDS the hard work is done - it's really simple to adjust the torsion value. Take the engine cover off. Just unclip the top cambelt cover and pull it out (fiddly around a rear sensor and fuel lines but it does come out). You will then see three 13mm bolts, slacken these slightly and then use an 18mm spanner to move the cam "inside" the pully. Only move it a FRACTION, not even measurably. I moved it a bit too much, probably only 2mm and the car would not start. Started flapping wishing I'd never touched it at this point. VCDS came up with a "outside plausible range" on the cam sensor. I reset this and got it back to where it was originally and it restarted at +6.6, tweaked it a fraction to get 0.0.
