1997 nisssan pickup 4 cyl. 5 speed. Truck runs fine at all speeds until the engine gets really hot (outside temp 100+ degrees), then engine sputters and will not take gas. Acts like old cars that had vapor lock. Pulled gas line off and seems to have good fuel flow thru filter and good pressure. When engine cools off, it runs fine again. Any ideas?

bad need of a tuneup? like new spark plugs, ?
172 , is 02 rich/ lean warning. this one is low oxy for rich.
this code can just be a victim. for sure , with misfire.
means 02 sensor stuck at rich,
what is water temp in engine coolant, at failure? less than 150F?
could be lots of things.
leaking injectors, bad fuel.
injector sticking> causing misfire.
id use a scan tool and watch all sensor when it fails.
too high fuel pressure.
misfires cold, but only luke warm cold starts not fully cold.

just one DTC, no P0300 or 30x misfire codes, not even P0300 pendings?

V6 or I4 engine? xe = i4?
bad tranny.?
low or too high ATF levels.
clogged bottom filter before pump, (shifts hot?)
RE4 trans is 4speed electronic
RL4 xxx trans is manual only
this side of your tranny has a tag is it RL/RE4 or or 3speed.

3 speed or 4 speed the FSM show four A/T used then .
there are 5 tranny total then ,4 AT (1 m/t)
on car diagnosis varies greatly by type.
fluid checks (if electronic the Tcm blink codes (DTCS)
pressure checks. for weak pump.
that stall rpm tests.
here is one used on your car
http://www.bulkpart.com/Merchant2/graphics/Catalog-pdf/RE4R01A.pdf

I would check the fuel pump.

When you run the engine, the coolant will remove heat and release it in the radiator. After you shut the engine off, the heat from the cylinders will still be there and the coolant will heat up some more. This is normal since there is no cooant circulating through the radiator.Without an actual temp gauge, there isn't any way of knowing just how much warmer it gets. I own a 1994 F 350 and have installed actual gauges. I can run my truck and watch the coolant temp. If I shut it off for up to 20 minutes, the gauge will go up ( sometimes as much as 20 degrees) when I start the engine, but return to the normal temps as the coolant is ciculated through the radiator.

you may be getting water in your distributor. check for moisture there.

Go to your local shucks or auto zone and they can check any codes behind your check engine light and it's free. It sounds like one of two things a O2 sensor or your mass airflow sensor but they will tell you for sure

did you check for vacuum leaks probably a vacuum hose thats been knocked off or eroded and needs to be replaced.

that is a normal rpm for the nissan pickup (hardbody)

Your engine coolant temp. sensor is going bad. What happens is that your engine computer is receiving a bad signal from the ECT sensor and it thinks it's 40 below. An example is it basically slams the choke shut if it had a distributor. When it cools off, I'll bet it runs just fine.

try running seafoam through your engine it will clean and can eliminate such problems