I have a 500SL (R129) 1990.
The car would not start, just back fired a couple of times. It started but was lumpy, had no power. I changed HT leads, spark plugs, rotor arms and dizzy caps. Car started on the button, and drove really well. I covered about 40 miles, no problem. A couple of days later The car started and ran well, but after about 3 miles it started to run lumpy, not a bad as before I renewed the HT leads etc.. but again it lacks power. It's as if it's not fireing on all cylinders and there is a petrol smell from the exhaust. Could it be the coil pack?