HI, I have a similar problem. I let my 1988 300SE sit for about 18 months. I moved it every couple of months, but recently it started running rough right after starting and dieing after 30 seconds or so, then it got so that it would not fire at all when cranked. By reading this and other posts, I jumped the fuel pump relay terminals and determined that the fuel pump was dead. I installed a new filter and fuel pump, and drained the old smelly gas. I added fresh gas and cycled the ignition switch several times to prime the pump (I can hear it run now). The car started and ran pretty rough for about 20 seconds then died. Now I can only get it to fire some when cranked
After reading the comments from Stevebfl, I looked for airleaks but didn't see anything. I loosened an injection line at the fuel distributor and turned the key so the fuel pump started. No fuel came out. I then pushed the airflow plate down and fuel came out. I then tried to start the car while pushing on the airflow plate. The plate was harder to push, but the car would only fire occasionally. When cranking the car normally the plate opens about 1/8th inch so it seems like there is not a large air leak. I took out a spark plug and it sparked brightly when cranking the engine. The car ran so well when I parked it, and it started several times since. I'm wondering if the old gas somehow clogged the injectors. It ran for a little bit after replacing the filter/pump. Any ideas about what might be causing it not to start?
Thanks!