92 Explorer 10mpg

My Explorer has 250K miles Mazda 5 speed Manual Trans is 4.0. Oil stays clean reciently started illuminating check engine light intermittently while at highway speeds upon decelerating. Any way using Snap on scanner at auto shop observed right bank auto rich code. Also observed purge can code. Other inputs verified such as good MAP signal, Good TPI, Water Jacket temps valid ect. Did the start up test was good. Cadalitic converter checked good for back pressure. Vacume pressure checked with in parameters. fuel pressure checked good and regulator no leaking internally. OK went ahead and replaced O2 sensor Bosh brand twice over six months, went ahead and replaced MAF per reccomendations of mechanic. Fuel economy 12 mpg if I really baby it. Smells rich, Plugs and wires changed also using AC plugs. Plugs and tail pipe black. Fuel rail holds pressure after shutdown and of course injestors are flow cleaned. Air filter clean. No obvious water consumption or vacume leaks. I am going to self test memory this afternoon time permitting. Can go back to mechanic but he is thinking verifing power at circuit locations then suggesting a new processer. I am in the self help mode before I go back. The other significant observation , when the MAF was unplugged the engine Idle did not vary significantly so is this this stuck in limp mode. Appriciate your time and I can help with reminding every body to be safe. David