Adding OBD1 ‘Style’ IABs Instructions


What are IABs?

IABs are the butterfly valves (similar to a throttle body valve) that are installed in Stock H22 and GSR intake manifolds.  They are activated electronically/vacuum assisted to open/close at specified RPM points by the ECU.

They effectively change the runner length of the intake manifold by opening a different set of runners when it is appropriate to do so from a long to a short runner to optimize flow through the intake manifold and speed up the air going into the motor.  This is good for N/A vehicles as well as Boosted cars but the effect will not be as noticeable as you are forcing air in on a supercharged or turbo car.

      What are the Differences in how IABs are activated?

With OBD1 Vehicles, (generally 92-95 year Civic/Integra, some earlier Accord/Preludes) IABs are activated by sending a GROUND signal out from the ECU, to the solenoid which ALWAYS receives 12 volts.  This ground completes the circuit and causes the solenoid to activate the IABs above a certain RPM and then deactivates it when it falls below that point (basically).

With OBD2 Vehicles, (generally 96+ years) IABs are activated when the ECU sends 12 volts to the solenoid from the ECU.  The solenoid has a constant ground and received the 12 volts to complete the circuit.

How do I make my Vehicle using an OBD1 ECU Activate the IABs?


OBD1 Vehicles

If your vehicle is already OBD1, all you need to do is wire a single wire from OBD1 Pin A17 to one side of a 2 Pin connector (that connects to your IABs) and the other side to 12 volts constant.  Read the OBD2 method for more info.  The process is basically the same.

OBD2a/OBD2b Vehicles

Many people are now adding IAB control to OBD1 ECUs like P28 ECUs or other converted OBD1 Civic/Integra ECUs and using those ECUs in OBD2a/b vehicles by using a conversion harness.  The simplest method in these ECUs which mimics the OBD1 GSR (P72) and H22 (P13) ECUs is to send GROUND from the ECU.

1) If you put an OBD1 ECU into an OBD2 vehicle though, you have some more work to do before you can activate the IABs via the ECU
2) Find the 2 wire connector that plugs into the IAB solenoid.  This is the same type of connector on the VTEC solenoid.  Generally it will be located underneath or on the side of the stock intake manifold
3) Next figure out which wire is connected to your ECU.  You can do this by finding a wiring diagram for your particular car and looking at wiring colors.  The universal way is to use a continuity tester.  Take one side of the continuity tester and touch it to ECU Connector A26 (OBD2a) or B16 (OBD2b).  You can also test on your conversion harness as well using OBD1 Pin A17.  Next touch either one of the pins on the IAB plug until you get continuity.  Remember this wire and leave it in the plug as is.
4) The other wire should be a constant Ground (OBD2 vehicles).  We need to change this to be a constant Power (12 volts).  To be sure, use a Test Light and make sure this is the ground wire.  Cut the wire away from the connector (give yourself some room to play) and tap it into a constant 12 volt source.  If you want to get creative you can connect it into the Dead End Plug that always has 12 volts provided to the injectors.  This plug is located near the drivers side firewall and is the plug most refer to when installing a resistor box.  You can also find any other nearby wire that has a constant 12 volts with the ignition ON but this is the easiest place to get power.  Once you have this wired up correctly, your vehicle is now ready to run IABs, OBD1 ‘style’
5) If you ever want to return your vehicle to stock configuration, it may be a good idea to use ‘quick disconnect’ crimp connectors.  Always be sure to use good shrink wrap and solder (or better yet, crimp) your wire connections in the engine bay.
6) If you are using a stock OBD1 P72 or P13 ECU, the ECU should activate IABs at the stock RPM.  If you are using a chipped ECU as most reading this will be, you can now modify at what RPM the IABs will open the secondary runners using an ECU that can control IABs.  You can test this and should feel a slight difference at that RPM.

If you have any questions or feel like I have left something out of this write-up, please feel free to email me at and give me your suggestions.  If you know the exact wire color for your particular car, please email it to me and I will add it to a list to make it easier for others!

 How to Install our IABs parts kit in your 1720 or 11F0 OBD1 P05, P06, PR4, P61, PR3 or P28 ECU

1) Install Q17 if not present (goes in directionally, follow other transistors on the board)…writing should face down in pic
2) Install Q34 if not present (goes in directionally, follow shape of white outline) …writing should face down in pic below
3) Remove R135 if present
4) Install jumper wire from Right Hand Side of R135 to Arrow Side of D13