I did the upgrade to a 120 amp alternator and I love it. I would recommend it, but first and foremost, you need to test your alternator. Changing the vr and ovp are just throwing parts at the car hoping to fix whatever problem you may have. Rough idle can be a number of things, but you have already pretty much ruled out ignition components, but you didn't mention changing the distributor and rotor. Check those visually and also test the resistance on the rotor to be sure. Next move on to the air system, since it's pretty easy to tell if you have a vacuum leak. Use a mityvac on the vacuum lines. Also grab a can of carb cleaner and spray it around the intake manifold and around the iacv while the engine is idling to see if there is a change in idle. After that move on to testing the fuel system. I have had several issues with my w201 which have pretty much all been resolved. Do a search on threads that I've started, I try to make sure I post the solution to a resolved post when I remember. Good luck and if you need he'll with the alternator upgrade send me a pm

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1990 190E 3.0L