'94 Camry V6 XLE
Got my CEL read today at O'Reilly's. Came back with:

P0135 -- O2 Heater Circuit Bank 1 Sensor 1
P0115 -- Engine Coolant Temperature Circuit

Here are the symptoms of misbehavior on this car:

The dash temperature gauge reads very hot. The radiator, thermostat, and the coolant temperature gauge have been replaced. I brought the car to my mechanic to replace the water pump too, but he used the infrared temp. reader to determine that the cooling system was operating at the proper temperature. The problem is somewhere in the wiring.

Also, the engine tends to hesitate and chug (like the mix is off) when the engine is cold. Once the engine heats up it accelerates fine.

Obviously, I need to replace an O2 sensor. Where is bank 1, sensor 1? What do I do about the coolant temp circuit?

Thanks in advance!