hi folks just share my experiencies,
had a problem with cold start, changed glow plugs (originals was good, I saved them) checked the wiring to glow plugs, positive poles form battery and fuses and the relay 103. The original with number103 was bad, bought a cheap one, what I checked and worked good when I checked, BUT the problem not solved. Under 10 Celsius rough cold start, at 11 Celsius everything OK. I lost. Used a year with this issue this winter and changed the starter, but it was a bad idea, it was a weak cheap french and rebuild the rebuilded bosch with my friend and took it back. Cold start not changed. Somwhere on VW forum I red, the cheap relay not working properly, so I bought a Beru GR081. Indeed changed the cambelt, waterpump and the coolant too. When i changed the relay problem solved. I was very happy. So my opinion need a good relay like bosch or beru and need to change the coolant too. I think with old coolant the CTS cant send a proper signal to the computer, what is very sensitive for weak resistant. I had an issue with coolant level sensor, cleaned inside the bottle a very thin copper stick and the problem dissapeared. I had before an A3 with abs problem (change the abs cube to used 500 british pound) but when I cleaned the fuses on the top of battery problem solved. So the resistance is very important. I hope can help to anyone