Testing the temperature sensor

Basic info - 1990 740 GLE Wagon - B234F engine. 125K miles

My temp gauge is extremely temperamental. Most of the time it's not
working but every once in a while it will suddenly wake up and decide
that it's had enough rest. That might last for a day or two and then,
just as suddenly, yawn and go back to sleep.

I feel it's a simply loose connection somewhere but, before I stretch
out under the dash, I thought I'd ask how to go about checking the
temperature sending unit. I think there are two of them.

Also, if that turned out to be the problem, would that tend to make it
run "rich"?

Thanks much,

Perk >)

 

The temperature sensor is a thermistor, the resistance can be checked
with an ohm meter and will vary with temperature. It can be tough to
catch intermittent faults though.

The other sensor is for the ECU and could indeed make it run rich,
however if both sensors are giving you trouble, I would suspect wiring.