89 suburban ,350, auto, tbi.starts fine runs at fast idle for 5 minutes drops off fast idle and dies will run with accelerator depressed, tried to read codes but just kept repeating 12 code. put ohmeter on tps got ascending and descending reading (13,14,15 each way) don't know if that's enough range. looked down in the throttle body , looks clean.
it's a rust bucket but other than the stalling problem runs great.

 

If it runs ok off idle but won't idle, I'd check the IAC system. You might remove the valve and clean off the pintle and try to clean out the passage. You can do an ohms test between the terminals on the iac valve, between A&B and then C&D, 20 to 80 ohms. You can do the same test between A&D and B&C, should be infinite resistance, no continuity.

As far as the TPS, the dark blue wire should be the signal wire. You can look for voltage on that wire. See that the voltage moves up and down smoothly as you work the throttle.