1993 Toyota Corolla Vacuum noise/check engine light

Dear sir, I am writing see what can be wrong. My check engine light came on and I did like suggested and had the codes read. I replaced the oxygen sensor, air temp, coolant, and map sensor. My car still sometimes seem to run rich. I somtimes will be driving and the check engine light comes on and then a strong vacuum sound happens and the light goes off? Is this an EGR vacuum solenoid or is it the throttle getting stuck open or shut? Maybe it's neither.