Although you repaired this problem by replacing the distributor, I would like to share a little story with you and the others in this forum.
I just went round and round with a family members 91. It would idle but would pop back and stumble under load. It got worse and worse until you could not drive it. They replaced the mass air flow sensor under the direction of the dealer and the cap and rotor to no avail. They brought it over to my house and we started digging. We were looking at the knock other wires the readings were good. The cylinder balance was in-consistent sensor causing the spark timing to be off. When I hooked my induction tech leed to one of the plug wires, I noticed the reading were all messed up. Onfrom hole to hole as well. The compression seemed even and the plugs, although a little sooty, were firing ok. I took the cap off again to look for carbon tracks even though the cap and rotor were recently replaced. There were no signs of tracks or any reason for the spark to be jumping around. I took the cover off that is under the rotor. This cover protests a thin 360 hole degree wheel. Not sure what it is for but a light passes through it to send a signal to something. The area under the sealed cover under the rotor was contaminated with a fine red dust. Probably from bushing wear. I gently blew the dust away with compressed air, put it back together and, low and behold, it ran great. So after $200 plus and lots of looking and exploring, a little cleaning off was the repair. Now it may come back and start missing some day and I might have to take five minutes and blow it off again, but it won’t cost them anything, and with over 200K miles on it, little repairs are good. For as deep as the knock sensor in on a 91 pathfinder, I'm glad it wasn’t that. As we were cleaning up the job, I noticed the power steering pressure hose had a pin hole leak in the top of the bend on the pump side, so we got to replace that this weekend.
Good luck with the head gasket. I have had good luck with a product called Water Glass to seal up a leaking head gasket. I was not wanting to put a lot of labor and money into the pickup as it was on it’s way out any way. But the leakage stopped.
Good Luck
Steve B.
