[Shotimes] Loss of power...

[Shane Graham]

Hello All,
 
I am a new member of the site.  I have owned a 91' SHO MTX for about 2 years.  I have done quite a bit of work to it since I have it, but enjoy working on it.  It has 130,000 miles on it.  I have a problem that I cannot figure out and need some help.  The car intermittently will lose power when driving.  It doesn't always happen either.  One day it could be fine, but the next day it may act up all the way to work.  It's like it loses 50% of it's power.  I can still drive it, but it is awkward.  And it will sometimes lose the power in pulses.  Like it will have full power for a split second and then lose it again.  It almost acts like it is being starved of air, getting to much fuel, or losing a few cylinders.  The tach does not drop to zero indicating a CPS problem ( I changed it and the Cam sensor about a year ago).  When I am idling in this state, the motor drops to 800 RPM and runs rough.  I have changed the fuel filter, swapped MAF sensors, put new Motorcraft plugs in, new plug
 wires, and put new valve cover gaskets and plug seals in (had lots of oil in the spark plug wells).  I am puzzled on what it could be.  There is also NO engine light coming on.  On one day I can race a Camaro and on the next I could get beat by a Yugo!  If anyone has any idea what it could be, I would greatly appreciate their time and advice!
 
Thank you,
 
Shane