HOLY MOLY…Replaced the PISTON RINGS??? Do you realize what you are saying with those 4 words?
Rings…are a SERIOUS “repair” Pathfinders piston rings usually outlast their owners and the vehicle before rings come into play…This is of course with basic maintenance and oil changes.
If your Piston Rings were actually replaced…Did they rebuild everything else while they stared at your engine completely dis assembled? Or don’t tell me they did the job from the Bottom Up and dropped the crankshaft out and proceeded.
I’m with many others here …and collectively we know MORE than A Lot about this stuff…
The piston ring replacement comment throws many of us into a bit of a tailspin…bec to do THAT job properly? Is called an Engine Rebuild…which suggests engine out and in pieces and every single physical connection to the vehicle to be temporarily UNDONE…until engine repairs dictate it goes back under the hood…then all the connections are Re Attached…
This leaves the possible causes of erratic behavior SO WIDE OPEN…that none of us will be able to really properly advise you on this. At this point in time…you need engine codes.
We would need a TON more info to direct you to a solution
Lets assume I IGNORE your piston ring comment… I would start leaning toward and engine misfire…oil leaking into plug wells…bad wires…Ignition stuff… Then move toward the MAF and other areas… This is IF we ignored the piston ring replacement comment.
But BOY HOWDY…when you tell us the “Rings” were replaced… REAL car guys here had a small “Kiniption”…I promise you that. Those 4 words basically throw all of our ideas into the “Possible” pile at that point. I also am suspicious as to how you were convinced to let them perform this “Repair” The bill should have been astronomical…and nowhere near a sensible type of thing to consider unless you were Born or Conceived in the vehicle and have unusually strong attachment bonds to the thing.