Quote Originally Posted by royster View Post
I had a similar situation with my '90. Replacing the throttle position sensor kept the light off, but I also replaced the temperatur sending unit...the one for the ECU, not the gauge. It sounds more like a faulty sending unit for temperature...a lot less costly: the TPS runs $135.00, (Rock Auto) though they eventually need replacing.

I also replaced the O2 sensor...all of this when I did a minor rebuild.

Not sure if the codes are the same for 94 and 90, but the code also indicates fuel pressure (check the fuel filter). An analog meter is $10 at Mal*Wart, you might as well invest in one so your truck can "speak" to you.
I'll see if the local Wally World has an analog meter. I have a fine digital one, but no good for this. Next time I make a Rock Auto order I'll pick up a temperature sender too. Is the one in the thermostat housing the one that feed the ECU, or does it do the gauge?
Thank you for the feedback, much appreciated!