The check engine light revealed it has to be replaced
Can I ,a very handy person, change the idle air bypass valve?
If so, some detail on 2004 Mercury Grand Marquis
Yes, it is really just 2 -> 8mm bolts and a gasket. Disconnect your battery negative terminal for 5 minutes to let the memory erase, then when you start your car, let it idle for awhile. It will idle faster than normal, then it will gently come down to a normal speed. Then drive your car, it will take a few miles for the computer to adapt to the new idle valve.
Thank you,did as you said & can't wait fot the better MPG!