I would take a hard look at the fuel distributor. My 87 420sel sat for 1.5 years and I had gremlins until I cleaned the fuel distributor with solvent to remove the varnish that had accumulated in it. I have never done this but I often wondered if running solvent thru the entire system might clear things out.
When a car sits, the fuel deposits varnish in the worst places. Areas like the little orfices and small screens in the fuel system components. I would take things apart piece by piece and clean them with a good solvent that disolves varnish.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k