For M119 engine, its idle is controlled by ECM, I don't think there is any idle rpm adjustment should be made.
There is still a way to increase idle rpm, by adjusting a plastic screw in the throttle linkage can do that, this actually adds tension in the linkage and is equivalent to applying some gas pedal pressure all the time, it can mess up the engine control and should not be attempted.
500 rpm of idle when warm is quite normal, lower oil pressure at idle is normal as long as it's higher than 0.3 bar and it increases when rpm is up.
You can increase oil pressure by using heavier engine oil, when I had 10W30 my oil pressure at idle was 0.4 bar, my idle is now 1.3 bar with 15W50.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.