quick stan
 

I have been told that carbon buildup on intake valve may be causing a cylinder miss at idle. What is the way to fix this? 1992 500sl

If you can find a place that sells Lubro Moly products, get some " Ventil Sauber " ( Valve Cleaner ).
My understanding is, it is about the best stuff. ;)

If you can't find Lubro Moly product, try BG44K, which is only sold through repair facilities. Sold at many dealerships and service garages. A can costs $21.95 in my area, but if it works it is a lot cheaper than the alternative. It is recommended to use this treatment every 15 - 20K miles

I am big on BG44k. I use it about every 9 months or so in our 3 cars. 6 cans just arrived today. I was able to get them for 73 dollars shipped. That's better than the last time which was closer to 90 dollars shipped.