My '90 240DL sedan is sputtering and backfireing when i bring the car off-idle. it will barely accelerate but it runs well at 55 to 60 mph.the exhaust smells a bit too rich.However it idles well, with only a small hiccup occasionally. I have replaced the plugs and wires, distributor cap and rotor. when i unplug the AMM and start the car, it idles well just slightly faster than normal but dies the instant i touch the gas. the problem begins after running the engine for about 2 minutes.

I just bought this car and i can tell when i get it fixed that im going to love it, its ran normally for me a couple times and was a joy to drive for that time. Any suggestions would be a great help, as i cant decipher where i need to start troubleshooting next.