Hmmm. You're not alone.

Check Engine Light

I don't have the answer for you from my experience. Since you're at the end of the line for parts-swapping and visual inspection troubleshooting methods, you may need some help tracing the trouble by probing the voltage the ECU sees and finds out-of-range. It is the same course of action I recommend to newmex999.

If this happened to me, I would rig a multimeter to the harness wiring at the ECU pin 13 such that I could observe the voltage on that temp sensor circuit until the OBD code finally gets set. How it behaves would steer me to the next step which would logically and rationally explain its behavior. I would then post my findings on the Brickboard for the benefit of others who might run into this.

The ECU grounds are indeed those often discussed, made under the bolts which fasten the fuel rail to the intake manifold. The sensor signal is derived from a 5V source, current limited by a 2.7K ohm resistor in the ECU.


--
Art Benstein near Baltimore

You can say any foolish thing to a dog, and the dog will give you a look that says, 'Wow, you're right! I never would've thought of that!' - Dave Barry