check engine light came on after rough idle similar to water in o2sx4 on 1996 Lincoln Town Car

new cat converter,throttle position sen,air filterand cleaned throttle has power just a really rough idle to point I have to put in netrual.i use premium gas and put stp fuel conditioner rich gas smell.could a throttle body get dirty that fast?does'nt explain check engine light.thanks for the last fix professor.please help

Asked by for the 1996 Lincoln Town Car