bhatt - just had the same thing last year on my 88 560sel - it's your fuel accumulator mounted by the fuel pumps in the back of the car - change it. For such a little part it sure is expensive - paid $287 CDN for mine but it cured the problem. If you do a search on fuel accumulator on this forum you will get much info to assure you that that is the problem. Please read the following thread in this tech help section " Hard starting on 1989 420 SEL " - you will understand
Morris