Ok... I was driving back my house after work, and stopped at lights.
I saw water temp constantly dropping down until it reaches 53C on my PFC!!!! and idle was dropping also....
WTF??
Lights turn green and started driving again and temp remains 53C, and about 20sec later it rises rapidly back to normal.
It did this about three times until I got home (2 miles distance maybe).
Didn't even touched the car... Getting sick of having problems now...

The turbo was recently de-sequentialed and had air pump removed.
I don't know if this effects the water temp to drop...

Is it thermostat stuck open? This is all I can think of...

Please help me if anyone know the answer to this problem.
Many thanks.

 

I'd check to make sure the car has the proper amount of coolant... it's possible the sensor is just seeing air at idle and dropping in temp for that reason.

just a shot in the dark I realize but maybe that's it.