what causes cylinders 5 thru 8 to misfire check eng lite flashes on 1998 Mercedes-Benz S500

on start up car has no power ran fine before problem started after been parked for couple of weeks

Asked by for the 1998 Mercedes-Benz S500
review when last tuned. it may be due.
rec. fuel system clean. ethanol treatment to 1 tank premium fuel. ethanol blend in fuel causes build up in fuel system, combustion chambers, exhaust system and causes increased wear to spark plugs.
rec. oil stabilizer treatment with next oil change. recondition cylinders and seals(improve compression).
1 more answer

I could be multiple things like a vacuum leak, mass air flow meter the left bank's O2 sensors...

Scan the codes.

Also inspect the engine harness for shorts and deterioration.

Good luck!