my 260E has the same problem as well. After spending loads of cash on the problem here's my sincere advice to you. If the car doesn't die when the idle is rough just run it till it's time to junk it. otherwise these cars can be a black hole for your hard earned money especially in problems where it's almost impossible to pin point the problem.
good luck !
Whether you think you can or cannot, Either way you're right!. by Henry Ford.