I had a misfire code come up on cylinder 8. i had mechanic replace all 8 plugs and the coil pack on cylinder 8. cleared the code but runs rough now, hard shudder at 40 mph. burns about a gallon of gas per 5 miles. mechanic said bad map sensor. replaced that but no change. still no codes coming up. what next??

 

As you know all vehicles are not the same, so how about a little more info ?

What engine in your vehicle and miles.
Can you have someone check for codes BEFORE shutting off engine?
Could you mean MAF sensor ? Big difference between MAF and MAP sensor..