I have 88 300E frustrated to the max. It starts and runs great for 10 to 15 min then it starts backfiring and chokes and dies. It started on trips and I put gas line freeze and good gas in it and it ran fine. Now all the time 10 min and she stops. Have replaced fuel filter ,fuel pump relay, new plug wires, spark plugs,drained gas tank and ran gas until it was pure. After sitting for 1 hour or so she starts fine and runs 10 to 15 more min. If you start her too soon (15 min) she back fires and won't turn over. Great compression Thanks for any help or suggestion on what to check next great car if she would run.

Try replacing the overload protection relay, costs about $70, located on passenger side under hood... Mine did the same thing until it was replaced.