My car is doing the same thing right now, it will stay at the N with the A/C on and that fan on full blast but as soon as I start idiling due to my WONDERFUL under drive pullies it starts to heat up.
No bubbles, white smoke, milkey coolant, etc - my head gaskets are fine.
I also have a boost leak on the SMIC, I'm wondering if thats supercharging the intake air charge so much that its causing my motor to run hot because the moment I let off the gas (NOT EVEN IN BOOST) it seems to run better heat wise.
My coolant sensor was also rubbish the last time I looked at it, the tstat was leaking and leaked on the sensor and corroded it but I just cleaned it off so mine could be bad.