"My 1997 F150 5.4 check engine light came and>
While idling or in Park the RPMs will drop below 500, then the RPMs will jump to about 1100 and then back down constantly,my gas mileage is terrible."

ANSWER: The above problem was fixed by replacing the EGR valve.


The check engine light started flashing (continuously), and when I would accelerate it felt like I was on a gravel road until I reached the speed-limit then it seamed fine, excluding the flashing CE light??? Many Thanks in advance for any help or advice.

ANSWER: The above problem still exist after the EGR valve was replaced. Guess what I took it to AutoZone and found a misfire on cylinder # 4. I'm presently going through the Haynes manual to find out how to change / test it.