Supra over-heating.

I took the turbo off and put it back on, now the car over-heats. Letting it cool down now to check the coolant level.

What could be the problem? HG is a 2MM Metal one with 25k miles on it.

It's doing it while just idling.

This may sound stupid but I didn't put the heat shield for the turbo back on yet, could that cause anything?