I started this thread in the Prelude forum and am not getting much response.

https://honda-tech.com/zerothread?id=2047513

To recap what was already stated in that thread:

1. Did an H22A swap into a 92 civic CX. I made entire engine harness myself using the connectors from the EG harness and H22 harness.

2. Since starting the car for the first time I am getting a CEL 3, which represents an electrical issue with the MAP sensor. The car runs very rich, which is causing the idle to bounce slightly.

3. I have tried 3 different Honda MAP sensors. They all do the same thing. I measure 5V and GND on the outside leads and the signal lead measures approx. 3V at idle, which is about right.

4. I have replaced all of the vacuum caps to the IM. Some of them were cracking from age. I also replaced the hose from the IM to the MAP because it wasn't as snug as I'd like. If there is any kind of vacuum leak anywhere else, will I get a CEL 3?

5. The wiring has been tested. With the MAP sensor connected, I get 5V, 3V and GND on the leads at idle. With the MAP disconnected, I get 5V, 30mV and GND with the engine off and key in the ignition position. Continuity from each of the 3 leads from the sensor to the ECU pins is good. I have less than 0.01 ohms on each wire. They are pinned in the correct orientation.

6. I have replaced the original P13 ECU with another good JDM P13. I get the exact same CEL, bouncing idle and rich condition.

At this point, I have gone completely through the Helms CEL 3 troubleshooting procedure. There are no other suggestions after replacing the ECU.

 

does the CEL pop up right away or after driving the car?

if it pops up righ away then despite your testing there is something messing with the signal from the MAP to the ECU.
Either wires that randomly short or open.
try running a temporary set of wires from the map directly to the ECU and see if it helps.

 

After resetting the ECU. I start the engine. After the RPMs go up from the initial ignition, then fall almost to 0. At that point the code pops up. The engine usually catches itself and begins to idle.

Almost 100% that I've already checked for shorts, but I am going to go over everything one more time. Running new wires was my last resort, but yes it appears that its necessary at this point.

 

bump becuase i am having a very similar problem with a D16Z6 in a OBD1 converted '90 Civic ran on a stock P28 ECU.

i only seem to get the code 3 under heavy load (ex. downshift to 3rd @ 55mph to chage lanes),
but i run rich (approx 25mpg, fuel pressure set to stock pressure w/ adj. FPR)
have strange idles (after putting car in neutral to slow down for red light i drop to ~750rpms for ~3secs, then drop to ~550rpms for ~1sec, then rise back up to ~750rpms),
and keep fouling 02 sensors and spark plugs (within ~1k miles).

also have slight bogging at low RPMs (below ~3000rpms)

 

i checked and re-checked the wiring to my MAP sensor and all is good. it is extended from the stock location (firewall) to the throttle body mounted location and switched to an OBD1 plug while i was at it. it also causes an occasional high and/or fluctuating idle. IACV has been replaced, timing is set to stock specs, coolant system bled...

also, just to give more info, my engine is a stock D16Z6 bottom end with a JG head (lightly ported head, slightly more agressive cam) and JG ported and tapered throttle body.