I doubt the MAF has just suddenly failed after a high speed run. It's more than likely an oxygen sensor than a MAF. Get the P code from autozone and go to an indi or BMW to get the BMW code. Make sure they match before you start replacing parts. Troubleshooting an air/fuel mixture prob (which is usually where the MAF comes into play) is not as clear cut as just getting the code and replacing it. Start by cleaning the MAF. You can get the cleaner at AutoZone too. CRC Mass Airflow Sensor Cleaner. Gray can. Just pull the MAF out and spray it down heavily. Let it air-dry for about 15 mins and then reinstall.

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