Have you tried BG 44K? Did it solve the rough idle problem?

My 92 400E does exactly the same thing right now, it has been idling roughly after cold start since this winter, now it's getting worse, however I don't feel the problem when engine warms up.

Can you let me the result?

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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.