I do not know of a relationship between the appearance of the ABS light and the blower slowing down at the same time.

Perhaps someone else can draw a relationship based on knowledge.

If you believe what you read here, appearance of an ABS light on an older M103 motor is usually indicative of a faulty OVP. This device among other things, powers up the idle controller, but you say your idle is fine?

I would at the least remove it and give it the shake test. If you hear anything rattling around, replace it. Others will tell you to open it up and solder whatever has come loose or repair a broken path. One tech who used to respond here(the one who started this site) once said in a thread that the OVP was not repairable. Who knows?

I would at the very least check out the OVP.

My 2 cents.

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'91 300-SEL