One problem related to gas recirculation valve (egr valve) has been reported for the 1998 Ford Expedition. The most recently reported issues are listed below.
Speed sensitive power steering: at the time of purchase the vehicle pulled right. The vehicle also exhibited a problem I call steering burst or hang. When turning either left or right the power assist steering would continue to apply pressure to the steering wheel. This continued pressure could only be stoped by jerking hard, back in the opposite direction on the steering wheel. Another issue experienced is when accelerating hard from a stop or passing etc. The vehicle moves to the right of the lane of travel. This occurs in a surprisingly quick and unusual manner as if the vehicle where dog tracking to the right. ?. The vehicle was aligned by the dearler 4 times in the first weak of ownership. Also the frame and the tires were checked. After the forth alignment I noticed the vehicle wondering left & right on the road. Suspecting somthing fishy, I took the vehicle to an independent auto shop. The mechanic ther pointed out visually the caster and camber adjustment slots and how they were maxed out. The caster and camber had been intentionally set to 3 degrees and 6 degrees out of manufactors specifications so as to pull left. Left so as to bury the pull right problem. This steering system is either mal-engineered, mal-assembled or has defective parts. A problem which the dealer nor manufacturer can resolve or don't want to resolve it. Ford had two of thier reps look at the problem. Both times they stated the vehicle operates as per design. The last time they (Ford & dealer) had the vehicle they deactivated the speed sensitve feature which makes the problem feel less apparent but is non the less still there. The power steering is now stiffer and tighter I can only surmise to further attemp to cover -up the problem. Other Expeditions I test drove had the same problem. And on the"Ford Expedition enthusiest" web site there are many of the same complaints. The a/c failure was catastrophic the vehicle had to be towed, late at night I might add. More details please call.