1995 Thunderbird p0402 code

What could be setting this code? I am getting rotten mpg and the car idles at 800 rpm and revs to 1300 and drops again over and over at idle. Any ideas?

Sure you don’t mean P0420?

Have your mechanic check the EGR. I show PO402 as “excessive EGR flow”, which is a good match for the lousy idle.