I have a 94 Park Avenue and having trouble with it stalling when you let of the gas. I have an Actron CP-9190, scanned it today and here is what it get; P0123 (TPS) and P0640 Quad Driver. I know that the P0640 is referring to the PCM, I also know what a TPS is. My question is, can a bad TPS cause the PCM code P0640 or vice versa. In other words can one make the other look bad? Let me mention, the car is OBD 1 with an OBD 2 connector if that means anything. I just got the scanner today, so just learning to use it.

You can test the TPS easy enough. This should help you do that. https://www.gmforum.com/trouble-shooting-test-procedures-141/testing-tps-throttle-position-sensor-279319/

Thanks for the tip. So a bad TPS could cause incorrect voltage control from the PCM?

I don't believe so. But you can also test the reference signal. https://www.gmforum.com/trouble-shooting-test-procedures-141/throttle-position-sensor-tps-signal-voltage-284385/