I had the same problem on 1988 190e 2.3. I even replaced the fuel distributor; although it was a used one. It turned out that it was the fuel distributor. What was happening is that the distributor was leaking and the gas was pooling on the butterfly on the air intake. When I would go to start the car it would dump the raw gas.

I change the fuel distributor with another used one it has worked just fine.

Hope this helps.

Gards