My 2001 Jetta TDI has started hard since the first day I bought it (2nd hand, private seller, 25K). Theres now 60K on it, and I've got it down to faster starting in 25F then in 75F, just by cycling the glow plugs, and especially by waiting 10 seconds after the glow plug light goes out before cranking (at colder temps). (This was definitely a good tip that I read about on here!)
Other than that, at temps in the teens, and lower, I still crank 6-8 seconds. Sometimes using the same technique at the same temp, cranking can be as short as 2 seconds (weird)...
But I've tried just about every trick in the book, starter, MAF, glow plugs/relay/harness, battery, timing, intake manifold, and she still gives me grief!
I have not replaced the coolant temp sensor which has been on my mind for awhile but never replaced as a MIL light never came on....
I was at the dealer recently explaining my problem, and heres one for you all that I have never heard: He asked if my fuel tank was ever mistakenly filled with gasoline..and that he's had a few people in who this has happened to, and the gas does something to the injection pump with the only symptom being excessive cranking, or no starting when its cold out.
He also mentioned theyre wicked expensive and he wouldn't recommend replacing unless it was a last resort...
Anyone EVER hear of this one? Not I.