A KE injection car will run very well without the added inputs of the O2 sensor etc.
The O2 sensor is there to fine tune the injection system for emission reasons.

The OVP powers the IACV, the cold start and the EHA circuit.
If the OVP is not working the car will be hard to start when cold and the IACV will not come into play.

Disconnect the electrical connector from the EHA and the car should idle very well. if it doesn't then there is something basically wrong with the H.V. electrical's or fuel delivery setup. If the engine idles too fast it maybe that the OVP is not supplying power to the IACV.

Just because the fuse is not blown on the OVP doesn't mean it's not faulty.