I have a 91 Maxima SE Manual- well maintained (350K miles - I know, time to get a new one!).

Anyway. it is still going great except for an intermittent problem for
the last couple years (which the dealer and numerous mechanics have
attempted to fix). After every few hundred miles or so the engine would
start to shudder and chug, not continuously, but then it could happen every few
miles. A couple of times it got so bad I had to stop and let it cool a
bit (at least it would shudder/chug all the way home). It could happen for a
few days in a row, then goes away for another few hundred miles of
driving (a week or two).

The engine diagnostics keep reading that all is OK (5 red & 5 green flashes).

I have replaced the wiring harness, computer, ignition cables, vacuum
hoses, distributor, fuel pump, fuel injectors and tested with a new air
flow meter, to little avail.

Any suggestions would be well appreciated

 

maybe its bad gas?

try using a different gas station for awhile...

 

Has the throttle body been cleaned? Is the O2 sensor original? How about the cat converter?

 

Gas is not the problem. I usually use Chevron 93 Octane
(cackles on anything less) and I have tried all the other brands.

The O2 sensor has been replaced twice, to see if the problem goes away - nada. I am going to clean the throttle chamber and check the cat converter.

The problem was more pronounced when the humidity is high (every time it would occur!). I found one of the vacuum tubes going to throttle chamber was loose. When I fixed this, humidity did not affect it as before.

Now it will happen under any condition but not as often (it ran 3000 miles after the humidity problem was taken care off, then it occurred quite often for the next 100 miles, then nearly 1000 miles so far, without incident......)