idles very fast,starts hard

There should be an overload protection relay in the right front engine area by the firewall, check to see if fuse is blown or failed relay, this will affect both of your problems. Jump starting the vehicle with high voltage or crossed cable usually cause this type of problem.

More likely an unmetered air leak into the engine. Look for loose air intake duct clamps, a tear in the intake ducting, etc. It's possible that the IAC is faulty, but if that were all it is, I'd think the engine would start easy, Unmetered air would cause hard starting. If you want to find a specialist, here's a directory link for you: https://repairpal.com/mercedes-benz-repair-in-taylor-michigan