LH 2.0 surging idle
 

1984 245 with 2.3 L and MT. It very suddenly started surging at idle and then dying at every stop when warm. I have done many things to isolate this issue and ran into a dark corner. When I check the voltage at the IAC valve while the engine is running, I get 13v at term 2-3. My understanding is, when the throttle switch opens, that voltage should drop to zero, and I should get 13v at 1-2. The voltage on mine does not change when the throttle switch opens. The throttle switch is properly adjusted and continuity checks out ok. The IAC is new, but it is a cheap generic part. I pulled the FI ECU and opened it up to look for burnt transistors or obvious faults. I have tested the AMM, O2 sensor, temp sensor. Replaced distributor, cap, plugs, air filter, fuel filter. Replaced most of the vacuum hoses with silicone, and replaced the injectors with rebuilt matched set of bosch OEM injectors. It smells while i'm driving very rich, like it is in limp home mode.
Do I need to start replacing wires in the harness (or the whole harness)? It looks like it has been replaced with a newer one already judging by the insulation. Ideas?