My ’91 Civic DX, 1.5L, Dual Point EFI, auto-trans, is throwing code 12 from the ECU. First, some history. I purchased this car about one month ago, and it had a blown head gasket, among other deferred maintenance. I removed the head and had it resurfaced, just to be sure it was flat. At this time gaskets, valve stem seals and necessary adjustments/repairs were performed. I replaced the thermostat, water pump, timing belt, misc. timing/drive belts, O2 sensor, ign. wires, plugs, dizzy cap and rotor, all rubber hoses and so on. I cleaned the IACV and replaced the PCV valve. I found the previously installed (old) PCV valve to be completely blocked. I ran the engine while still on jack stands for about two hours total, after which I changed the oil and filter. On its first drive following the above work, code 12 was thrown by the ECU, two blocks from home, even though it did not throw this code or any other while I tested it during the initial two hour run. I reset the ECU and it ran fine for another couple of blocks and threw the code again. I looked up this code in my Haynes manual and it tells me it pertains to the EGR system. I have searched for an EGR valve or whatever they use in place of it to no avail. All I have found is a cluster of relays and such near the firewall, on the passenger side, above the fuel filter.
Lastly, after chasing each of the vacuum hoses to their respective connecting points, I noticed that hose 16 was disconnected and the end capped with a screw, which was just shoved in. I haven't a fog where this vacuum hose connects to. There is a cover plate held in place with two bolts, covering an opening on the cylinder head, near the distributor flange. Is this the mounting location for the EGR valve? There is nothing there but the cover plate at the moment. But I also don't see any additional (spare/disconnected) electrical connectors in the vicinity.
Can someone please give some suggestions as to what to look for?