Totally agreed with Lebenz.
I just cured the stubborn rough idle problem on my 92 400E by adding one bottom of Pennzoil fuel system cleaner and cruising on the highway on 2nd gear for a while.
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.