Mystery Overheating Issue

[Shakester]

I have a 2002 B6 with 100K thats overheats while idling. Okay, maybe overheating isn't the exact word, but the temp on the gauge goes up to 3/4 and pretty much stays there until I start driving again. At long lights, I usually just gas it a few times and the temp will go back to normal so I'm assuming it has something to do with coolant flow. The waterpump was replaced a few months back along with the thermostat, but just in case, I put a new thermostat in there but it didn't do anything. I replaced the radiator and that didn't work either. I blew out the heater core with a nice stream of water as well. So now I'm stuck and so is my mechanic. I've suggested the coolant sensor but he mentioned that it would at least throw him an error code. We've check all the hoses and all of them are clean. I've read a few forums and have read about problems similar to this, but the solution has always been the thermostat or waterpump, which isn't the case here. Any ideas or help is hugely appreciated. Thanks!

[Audi Skate Snow]

fan.

[heywier427]

^ and the relays that operate it.

[Shakester]

This issue is really stumping my mechanic. He didn't get any VAG errors so he was sure it wasn't the fan relay. He ran the car until the temp started to climb and he checked the fan. The fan was working as it should but the temp kept climbing. He shut the car off for about an hour then started it up again. This time, he just let it idle for about 45 minutes and the temp stayed right where it should. So he decided to drive it around the block and right when he got out the garage, the temp started climbing. He's getting fustrated as am I. So it doesn't look like its the fan as suggested, but I appreciate the advice and would appreciate any other solutions. Thanks!

[Chillmode]

Low on coolant? possible coolant reservoir leak?

[Shakester]

Coolant level is fine and no visible signs of a leak. When the temp gets up to 3/4, the Low Coolant flashes, but once I start driving, it goes away as the temp falls back to normal. While I'm stopped and with the temp climbing, I can just rev the car (while in neutral) and the temp will go back to normal as well.