My 1991 190e would at first take about a dozen tries to start and eventually start and run fine. Now it does the same thing but will stall out after about a mile and not start again for about an hour or so if I am lucky. I hear the hum from the fuel pump when it starts up like it is working. I do not know if that means both are working. I did notice the caps on the two small vacuum lines attached to the fuel pumps are all falling apart. I also noticed that there is no pressure on the fuel cap when it is removed. The fan belt is also loose if that makes any difference. The nearest person who knows anything about mercedes is 50 miles away. Any ideas will be appreciated.