Chibong,
There is also vw diesel list which is of course more focussed on diesel
issues, not that we have many problems, only desires for more hp. There
is an average of 10/15 messages a day. If you want that list information
then contact me.
You say that it is hard to start at -6C, does this mean that it
eventually starts, has a very rough idle and eventually runs regular
after warming up? Does the operation of the cold start cable change the
quality of the hard starting?
Most likely one of the glow plugs is not working.Its the first place to check
At -6C I would not be able to start up with two not working.
When the engine is stone cold, turn the ignition key to ignite the glow
plugs two or three times, place your fingers directly on the block
around the glow plug and you should feel the heat from a working glow plug.
Its okay to change all 4 plugs anyway, once you do this job you will not
want to do it again, ever.
Replacement plugs, I was supplied with NGK Y-901R 11V by the VW shop,
only one of the four lasted more than 6 months. I reused my 3 old plugs
but still working, part nr, 205 201 032 made in France, they are at
least 8 years old.

Check the voltage at glow plug nr 4. It should read 11.4 v or so.

Other lesser possibilities, ice in the fuel, air in the fuel supply,
would both give similar hard starting symptoms.
Report back,
Good luck, Martin Kennelly