All common Honda and Acura D and B series engines use a 2 wire Idle Air Control Valve (IACV). The 2 wire IACV uses one wire for power, and the other wire is for the idle control from the ECU. However, Honda made an exception to this on the 99-00 Civic DX and LX, and on the 99-00 Civic EX with automatic transmission by using a 3 wire IACV on these models. The 3 wire IACV has one wire for power, the second wire for ground, and the third wire for idle control from the ECU.
All of our chipped/tunable OBD1 ECU solutions for the 99-00 civic use an ECU that is setup for a 2 wire IACV only. This makes it necessary to convert your Idle Air Control Valve to a 2 wire style IACV anytime one of our tunable/chipped OBD1 ECU's are used.
The first step is obviously to switch out your 3 wire style IACV with a 2 wire IACV. This may require an intake manifold/throttle body change if you still have the stock engine installed. If you have done an engine swap with a B series engine or other D series engine that already has a 2 wire IACV, then this will already be taken care of. If not, you will need to install a 96-00 civic EX with manual transmission intake manifold, throttle body, and IACV or similar.
Here's how to do the wiring:
You will need to source a 2 wire IACV plug to replace your 3 wire iacv plug, and disconnect the ground wire from your idle air control valve wiring and re-pin the signal wires at the ECU plugs. Here's how:
At the IACV plug:
1. Cut the orange wire and disregard it or tape it off. It will no longer be used.
2. Connect (solder/heatshrink) the yellow/black wire on your engine harness to the green/black wire on the replacement 2 wire IACV plug.
3. Connect (solder/heatshrink) the black/blue wire on your engine harness to the black wire on the replacement 2 wire IACV plug.
At the ECU:
1. Locate connector "B" at your ECU.
2. Move the black wire with a blue stripe from pin B6 to pin B23.
3. Remove the orange wire at pin B15 and do not reinstall. Simply tape this wire aside as it will no longer be used.
Your engine and wiring is now setup to use the 2 wire IACV plug. You can now connect your OBD2B to OBD1 ECU Jumper Harness and plug in your OBD1 ECU.