CHT difference

[lancair390]

When I start my engine CHT3 does not climb as usual and shows lower temps.
All 4 CHT's start with the same temp, only CHT3 climbs slower.
After 3 minutes and alway with 180°F it goes in it's usual range and stay's accurate the rest of run up and flight.
This happend on my last 15 flights. Before all was normal. (EE4500)
Is this a sensor or wiring problem?

Christian