Nissan Repair: 1996 Nissan PU XE, shaft seal, compression rings

Question
I am trying to fix my sisters 1996 Nissan PU.  It first showed several code at Autozone.  Kwick Lube did an injector clean.  The problem we are having is very frustrating.  After driving several miles, the vehicle begins to act as though it is starving for gas, it looses power the jerks and goes again.  There is no particular speed that it does this.  Say id you were traveling 60 mph and the traffic in front began to slow, so you come off the accelerator for just a short time, then give it gas again to maintain your speed, it will loose power then all of a sudden accelerate.  After injector cleaning at Kwick Lube, remembered they did not reset the computer, so I did that today and check engine went out.  Took back to Autonomies; was advised the only code showing was for the throttle sensor.  Bought one, disconnected battery, replace with a new one, reconnected battery, check engine light went back out, but problem still remains.  Please help!
Thank you, Pat

Answer
Patricia,

I would think the distributor is acting up as if it had oil on the optics.  The vehicle uses an optical shutter wheel and an LED pickup and receiver.  These are under the distributor cover.  To gain access the cap, rotor, toror post and cover have to be removed to check for the presence of oil.  The problem, after many years and miles the shaft seal fails on the distributor allowing oil to migrate up the shaft and onto the optics.  The situation is compounded by blow-by from the compression rings getting weak over the years.  The result is the optics get coated and it messes with the ignition firing the plugs and you get the cutting out followed by running and so on...