I believe you have stated that throttle control works correctly except for the eco switch not raising the engine idle speed, suggesting that there's nothing wrong with the throttle motor or carb. With the inverter module being potted, any repair would be close to impossible. Certainly infeasible. I'd expect that the eco switch merely connects to pins on the computer chip inside the inverter module, as opposed to leading to some discrete component that could be replaced if it weren't for the potting. The good news is that it's high probability that the problem is in the switch, wiring, or a connector.