Replace pre-cat O2 sensors ^^
Clean the MAF sensor with CRC MAF Sensor Cleaner.
Make sure tire pressures are correct.
Clean your throttle body
Also make sure your water/coolant temperature sensor is plugged in!

Question: did it only exhibit this behavior after the extensive service?

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean