Per the OPs initial post, "occasionally the volume of airflow will suddenly diminish".

This symptom is not caused by icing or compressor disengagement.

Icing will cause a gradual loss of airflow (and a long low flow time cycle).

Compressor disengagement will usually not effect flow at all, only warmer air flowing.

Sudden loss of airflow symptom is classic FSR malfunction condition.

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!