Was moms car and well taken care of ..154,673 miles ... in last couple days idol won't drop or raises on it's own ..rescent tune-up and timing belt replaced .. if i shut it off it goes back to normal

What is your question?

Problem is intermittent, injector cleaner is used every other fill up .. There was an after market O2 sensor installed several yrs back and check engine light comes on occasionally .. when tested comes up same every time

How long has your 1995 Mercury Tracer had this problem?

Few days