Just noticed this in the S4 FSM this morning. Don't know whether the S5 is the same.

The S4 has a "Hot Start Assist" feature. You may know that the vacuum to the fuel pressure regulator is switched by a solenoid controlled by the ECU. The fuel pressure is reduced at idle by this switched vacuum. The idle mixture is tuned using this lower fuel pressure.

The Hot Start Assist feature is that if the ECU senses a hot intake manifold air sensor at startup, it will leave the fuel pressure vacuum turned off for 90 seconds, thus richening the mixture. I presume that after 90 seconds the air flow should have cooled the air temp sensor sufficiently to provide an accurate reading.

So if you don't have your fuel pressure regulator connected to the switched vacuum you might try that.