Either post a picture of your engine or post the VIN number. Should be able to tell from the VIN number. I could tell you which if I saw a photo of the engine.
Also the 8 valve is single overhead camshaft and the 16 valve is dual overhead camshaft. The 16 valve will have 2 roundish humps ( approximately 5 or 6 inches in diameter) at the from of the cam (valve) cover.
There were no 16valve 2.3 4 cylinders made in 1991. The Cosworth 2.3/2.5-16v was made for the US in1986/87 only.
Looking for a Used 190-Class in your area?
CarGurus has 21 nationwide 190-Class listings and the tools to find you a great deal.
Search Mercedes-Benz 190-Class Questions
Mercedes-Benz 190-Class Experts