Power Loss of Mercedes W221 S320 CDI 2007 model

Hi 

My car (Mercedes S320 CDI W221 2007) has done 75,000 KMs and for last 6 months there is this very strange problem.  

After every 3-4 days the car looses power and drives very heavy as there is some extraordinary weight on it and after i use a blower to clean engine compartment it again regains power and drives very light (blow air).

Before and after is huge difference in car power.

I am not a technical person but i suppose there is some exposed censor which get dusty or something or some electrical connection problem. 

Star diagnoser is not showing any trouble.  

Can you guide what can be the cause or what should i look for. 

Thanking you in advance.