I have a B16a swapped into a 91 CRX HF running an OBD0 PR3 ECU. The IACV does not work when I have my PR3 ECU installed in the car. I've cleaned it out and checked the wiring, even tested it, and it seems to work fine; it just doesn't get actuated correctly by the ECU. Unless I induce a vacuum leak the car will just stall once it warms up (since the PR3 is leaving the IACV closed). When I install a PM6 though (CRX SI ECU), the car idles great. ....So it's something with the ECU itself. The PR3 definitely recognizes the IACV, if I unplug it while running I do get a check light, it just doesn't ever actuate it. My understanding of the IACV is that it's simply a pulse-width modulated solenoid. Power is supplied constantly to it on one side and the ECU simply grounds the other side when it wants the IACV to open (raising the idle). Does the PR3 operate differently? Like does it ground the IACV when it wants the idle to drop? Or do I most likely just have a bad ECU?