Cylinder 4 misfire, TPS low voltage

I posted on this forum for the same problem but now I have a few more details.

The problem I'm having is with my 2002 Mercury Sable DOHC. The engine light is illuminated and I had the codes read. I get misfire on cylinder 4, TPS does not match MAP sensor, and TPS low voltage. The TPS has been replaced (twice) so I'm confident the TPS sensor itself is not the problem. However, I tested the voltage on the sensor by backprobing the connector. Here's what I got:

The reference voltage was 5 volts (normal according to my manual)
The signal voltage was about 0.37 with throttle closed. I had a friend open the throttle gradually but the voltage didn't budge at all. I know this is the problem now but what would cause this?

Also, my manual says the signal voltage should be under 1 volt when the throttle is closed but should it be closer to 1 v than 0.37? Please give me a reference where I can see any information you give if you can.

Update: I replaced the wiring harness hoping that there was a short or some other abnormality there that was causing the signal voltage of the TPS to remain constant. After replacing the old connector with the new one there was NO CHANGE.

Now I'm thinking either the PCM is messed up (but i don't know how because the reference voltage is right at 5V) or the TPS is bad (but like I said, I replaced the TPS twice recently) I guess there could be a short in the wires further down than where I cut for the new TPS connector too. Anyone have any ideas?