I'm betting it's the 8 valve, since I wonder if anyone accidentally ever bought a 2.3-16. It would be like going out to buy a Mustang and accidentally buying a Shelby or Boss 302. The owners manual is easy to get, either on Ebay or at the dealership/MBUSA. I would strongly suggest that you pick up a copy of the Haynes motor and chassis service book for the 190E as a reference. It doesn't cover the whole car (hvac and trans are notable omissions), but it's a comfort when you don't know where to start.