"190guy" stick with the copper plugs and watch the fuel consumption, If you see a drop then start looking at other things. Contrary to popular believe platinum plugs are not all they are cracked up to be on an older benz engine. If you have a variably timed engine then they work ok. But our pre 90 engines just detest them. I have heard more stories against them than I have for them on these engines. Also change your OVP its good insurance to do this. Finally check the condition of your fuel pump relay (the rectangle box next to the OVP) and do a fuel pump pressure test. Your temperature sensor is also crucial to start up. Do a search on all these things I have mentioned and you'll get lots of info for you to check.
Of course non of this advice can substitute taking the car to someone you trust who knows them well