The engine (at least the M103 sixes) will get pretty warm at idle in the summertime. 100-105 is pretty normal. Mine will get up to 110 with the A/C on and it's 100+ outside. As long as it doesn't hit the redline...

Is your fan clutch working okay? Couple of ways to check - does it engage when you first start the car and drive off? Is it engaged after sitting idle for a couple of minutes (and when the coolant temp is 105+)? You should get a pretty noticeable roaring sound from the engine fan when the clutch engages.