Mazda Repair: suspension, front end vibration, fuel mileage

Question
My 90 929s just had all 4 struts replaced due to a strange fairly significant front end vibration which occurs out of the blue unrelated to road conditions and disappears upon stopping or slowing down and can be driven as many as a 100 miles before doing it again. Nothing is different than it has been for the last 180k miles as to the steering or handling except I have noticed once or twice a slight intermittent vibration similar to a tire slightly out of balance, but this does not always lead to the steering wheel shaking  pretty violently problem I've had now three times in the last week.  Thanks for your previous help. Turned out to be a defective oxygen sensor that took a while to figure out when it didn't solve the fuel mileage problem.

Answer
Sounds like you have slack wear in the steering somewhere.  Likely a tie rod end (inner or outer) or within the rack unit itself.  This could cause the front wheels to oscillate slightly at speed (usually at or around 40-50 MPH).  It may come and go due to the road conditions, pitch, turns, etc..  If it is a worn part in the steering it will get more and more pronounced over time.  Stepping wear on the front tires is a common sign of this.  Due to the power steering hydraulics the feel is normally dampened through the steering wheel so you may not feel the oscillation behind the wheel.