I purchased a ver clean 89 420 about 3 months ago. The check engine light camo on shortly after I purchased the car. I replaced the 02 sensor and all of the ignition parts. Now the car starts ok but in the city the check engine light comes on and it misses and runs rough. I take her on the highway and she runs like a champ. Could this be a fuel problem. Does anyone have any suggestions?

Thanks,
Dan