If you're running an F23A with an OBD1 ECU, there is one important part of the conversion that is often overlooked:
The factory 3-wire IACV must be converted to a 2-wire OBD1-style IACV.
The original F23A uses a 3-wire Idle Air Control Valve. A standard Honda OBD1 ECU is designed to control the older 2-wire IACV, and the two systems are not directly compatible.
Simply installing an OBD2-to-OBD1 ECU conversion harness does not convert the IACV.
You Cannot Simply Rewire the 3-Wire IACV
This is not just a matter of changing the connector or combining wires.
The OBD2 3-wire valve and OBD1 2-wire valve operate differently. The factory F23A 3-wire IACV should not be connected directly to the OBD1 ECU and expected to work correctly.
The engine needs to be physically converted to use a compatible 2-wire IACV.
Depending on the intake manifold being used, this may require an IACV adapter plate or another method of mounting the 2-wire valve.
What Happens If the IACV Isn't Converted?
If the ECU cannot properly control the idle valve, you may experience:
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High idle
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Low idle
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Surging idle
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RPM dropping too low
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Stalling when coming to a stop
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Poor cold-start idle
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Check Engine Light or IACV-related faults
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Little or no ECU control over idle speed
These problems cannot be corrected properly through tuning if the wrong IACV is still installed.
OBD2-to-OBD1 Harness Does Not Handle This Conversion
An ECU jumper harness allows an OBD1 ECU to connect to an OBD2 vehicle harness, but it does not automatically make every OBD2 engine component compatible with the OBD1 ECU.
The IACV is one of those components.
For an F23A OBD1 conversion, make sure the engine is using a 2-wire OBD1-compatible IACV before trying to diagnose or tune an idle problem.
Before Ordering an F23A Tune
If you're ordering an OBD1 tune for an F23A setup, verify that:
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The vehicle has been converted to an OBD1 ECU
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A compatible 2-wire IACV is installed
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The IACV is wired correctly for the OBD1 ECU
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There are no vacuum leaks
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Base idle has been properly adjusted
The factory 3-wire F23A IACV is not compatible with normal OBD1 ECU idle control and must be converted.
DGTune specializes in Honda and Acura OBD1 ECU tuning, chipped ECUs, ECU socketing, and remote tuning.