If your economy gauge is "barely in the red" you have a vacuum leak. The economy gauge should be pegged to the full left at idle. Find that leak and fix the last of your problems.

Look behind the engine in front of the firewall. On my V8 (1988 560SL) there is a primary vacuum tap into the intake manifold at that location. That is a location of max heat and oil and the rubber connector deteriorates often. It is often overlooked since it is hard to see.