87 4Runner, 22re
It appears it is probably a bad ground in the dash gauge causing my gauge problem.
DIRTDEVL replied: 'This was discussed once before on here a couple of years ago. The thread had pics of where to add the ground, and everything you would need to know about doing the job.' Anybody have that info?

The gauge grounds through the water temp sending unit. That's a yellow green wire.

There is a combined ground with the fuel gauge, a white and black wire. Grounded over at the left front pillar.

The hot lead coming in to all the gauges is yellow.

To measure the sending unit, the resistance should be 146.6 at 140F, and 24.3 at 239F.

To check the gauge, measure resistance between the following points on the dashboard gauge cluster.
IG-TU 135
TU-E 138
IG-E 273

The gauge grounds through the water temp sending unit. That's a yellow green wire.

There is a combined ground with the fuel gauge, a white and black wire. Grounded over at the left front pillar.

The hot lead coming in to all the gauges is yellow.

To measure the sending unit, the resistance should be 146.6 at 140F, and 24.3 at 239F.

To check the gauge, measure resistance between the following points on the dashboard gauge cluster.
IG-TU 135
TU-E 138
IG-E 273

I was having a problem with my temp gauge in my 85. It would read right in the middle upon startup (when cold) and then drop down to zero after a few minutes and then move up and read normally after the truck was warmed up. In the process of fixing my gas gauge (unrelated problem) I had the gauge cluster apart so I pulled the temp gauge and tightened the connections on the back of the gauge itself (two threaded posts and a nut, I believe).

It has been working properly since doing this so I believe I had a weak connection on the back of the gauge, where it mounts to the circuit board. You might try it if you have to take the gauge cluster out anyway.

Allan

Thanks guys...I'm divin' in.