Cant figure this out!!!

Ok.... I own a 300e 1988 and last week it was running like crap. Like it was really hesitating and bogging out. So for starters I replaced the spark plugs with bosh plat. 4s and the wires. It ran fine. One week has passed and now it is back to the same thing. It feels like it is flooding it self out. Sometimes it even backfire in the carb. It is bogging out big time. When you push on the gas it barely goes and then it will catch (sometimes)and take off. Why did it run so smooth for a week. This is really weird. Did the plugs go bad that quick...and if so ...why? Please help if you can.

WasHappy