Have a 85 190E. I took it to the local dealer because of of rough idle and a shake when I would step on the gas. They found that the #4 cylinder was misfiring and determined that it was running rich. Spark plug was also carboned up. They replaced the fuel injectors the resistor boot and the plug. It worked fine on the 45 minute drive home. After a couple of hours of sitting I went to run errands and the car was acting the exact same way as before, like I had never taken it to the dealer. I checked the #4 plug and it was all corboned up - again. Any ideas on what this could be? Thanks for your help.