1997 E420 M119 Engine Question
 

While I was changing to spark plugs, I noticed a black rubber-ish hose that connects from the top of the intake manifold to the top of the right (passenger side) exhaust manifold was all soft, full of cracks and almost fallen completely apart to pieces. What is this hose for ? The car seems to run fine and normal even with this hose not connected ?

Please help and TIA for any answers.

That would be your crankcase breather / PCV hose.

Definitely replace that hose. With it disconnected, the crankcase is sucking in unfiltered air (that's why it comes from the intake manifold).

Furthermore, when your load is mid to high, the flow of air reverses, pushing blow-by gasses from the crankcase to the intake. So, without it connected, your intake is leaking vacuum, sucking in air from the hot, dusty, engine compartment, bypassing your fresh air ram intake and air filter.

Plenty of online retailers sell it. About $25 bucks, give or take. Part number 1190901982.

Yeah, mine was disintegratd after 160K miles which I replaced.

yea mine is getting loose it is original like 4 sections,I see the new ones are one piece less leaks! trying to plug up all the vacum leaks at 259K