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Hey all, I have a K24A2 swapped Miata (Accord ECU / Element Harness) and I'm trying to diagnose a chronic issue with the IACV control. From what I have gathered, I hypothesize that the valve is not being properly controlled by the ECU.

Symptoms:

• Low Idle at cold start (~1500 RPM, target 1800 RPM)
• High Idle when warm (~1100 RPM, target 800 RPM)
• The ECU pulls timing to -2deg when warm to attain the above numbers. Rich fuel mixture at idle seemingly as a result.
• I am able to kill the engine by pinching off the air flow to the IACV. I don't suspect any vacuum leaks.

Diagnostics:

• with the IACV connector disconnected and the car keyed on, measured 12V on the center pin, ground pin continuity to ground, 12V potential difference between center power pin and ground pin, 12V potential difference between ECU control pin and ground.
• got a cheap-o oscilloscope to measure the control signal PWM signal. I wasn't able to pick up a trace, but it is unclear if that is because the ECU is not firing the correct signal, or if the tool is bad.
• Disconnecting the IACV seems to make no difference to the idle function.
• Connecting a different IACV to monitor valve operation indicates no IACV motion throughout the warmup process.
• Flashing a different base code seems to not improve idle function. If anything, idle ignition timing is more erratic.

Any suggestions or things I may have missed? Thanks in advance!

What Accord ECU? What codebase are you flashing? If you're not seeing error codes for the IACV when disconnected that makes me think it's disabled or you're on the wrong codebase. TPS needs to read less than .5 in order to go into idle mode.

I have a 05 accord ECU (37820-RAD-A54)

I made sure to not disable IACV in settings

It’s possible when the engine was tuned, the wrong codebase was used. I suppose I can try copying ignition/fuel/cam maps to a new accord base tune and see if that fixes it?

I made sure to zero the TPS before proceeding.

You can only disable IACV using the PRB/RSX codebase, so I'll assume you're using that. An RAD ECU does not have a check engine light output, so are you manually checking for error codes anyway? Is the TPS reading zero when closed and idling?