My Mercedes had a problem leaking coolant but I replaced the water pump and fixed it. I noticed sort of a irregular idle but chalked it up to being a problem with the water pump, well a few weeks after I replaced the pump I pulled into my driveway and the car started chugging horribly! I shut the car off and when I started it the next day it hardly ran (chugging) so I turned it off and tried to start it again but now it doesn't start unless you push the accelerator to the floor then it does not stay running if you take your foot off the pedal! I pulled the spark plugs out to inspect them and 3 looked good and 3 were black what does all this mean??