Ford Repair: ford escort engine irregularity, mass air flow sensor, mass air flow

Question
My 1993 5speed Ford Escort has 105,000 mostly highway miles, timing belt replacement at 80,000 and gets good milage.  About a year ago, the following symptoms arose.  While driving between 55 and 65 mph, the engine acted like it's starving for fuel or running on 3 cylinders.  When mashing the accelerator, it surges forward and then easing up on the accelerator the front end shakes violently.  You have to drive through the shaking by easing the accelerator to the floor.  If you drive faster the shaking doesn't happen, nor does it happen under 50 mph.  Ford did a diagnostic on the road and found that when the shaking is occuring there is no electrical activity across the O2 sensor.  So far, the plugs and wires have been changed, the mass air flow sensor, coil pack and the O2 sensor have been replaced and the problem still occurs between 55 and 65mph.  The Ford guy says it must be a sticking valve or lifter and would require an engine rebuild.  This sounds funny to me that an electrical short during the shaking is caused by a mechanical issue such as a lifter.  Could there be some other sensor or electrical component malfunctioning?  Otherwise, the car runs fine, the problem only occurs during highway speeds of 55 to 65 mph.  Thanks.

Answer
Phillip,

This is hard for me to diagnose without being able to drive the car, but what concerns me most is the shaking of the front end.  Are you sure you don't have a tire or front end problem causing the shake?  If it is engine related you should be able to duplicate it at a lower speed in 4th gear and a higher speed in 5th.  

As far as no electrical activity on the O2 this is usually caused by a lean condition pumping oxygen into the exhaust, not by a shorted wire.  Yes, a floating or sticking valve could cause this, but not usually to the extent you have described.

Good Luck!!