Dec 23, 2005 · TDI. Skoda Octavia '01, TDI 90. Nov 17, 2001. #1. Hi all! Some may remember my very theoritical thread about the coolant glow plugs and under which conditions they were turned on. After some experiments, I discovered that the IAT (intake air temp) that triggered the thing was about -10°C on my ECU, provided the coolant temp was under 55°C.