Engine Problem
 

I own a 1994 E420.
If I let it sit for 7+ days, it starts without a problem. After about 2-3 miles, the engine begins missing, power is lost and it will backfire. This has happened 10 times in 18 months. If I shut it down, the catalytic converters snap, crackle and pop. If I let it sit for 5-6 hours, it runs fine. My mechanic says it shows 'no codes'.
I can't believe this is the only E420 that has this problem.
Any/all advice would be appreciated - I really love this car!
Robert