My 5.4 ford engine with 6 speed transmission does not run smooth between 35 an 40 mph. The rpms fluctuate. Is this normal?
Is that a speed at which you often cruise. If so the throttle position sensor would be my first guess. Have you had the computer scanned?
I have noticed the fluctations afetr coming down a hill and taking my foot off of the gas. I have not had computer scanned yet. Thanks for you reply.