High temp is probably the magnetic fan clutch switch, a temp sensor located at the front of the block (red?) that has failed. Check if the engine mounted fan spins up when the engine idles and the temp rises. If not, remove the wire connector and "short" the pin holes with some insulated wire and see if the fan clutch engages while the engine is running.

Your idle issue could be many things . . . vacuum leak . . . bad idle controller valve . . .