91 civic CEL code 4
 

Just changed my engine to another stock correct engine with fewer miles (mine had 450k miles on it) d152. Car sets a code 4. My info shows distributor. Possibly a wiring problem. The symptoms are ... on start up the cars idles terribly when there is no cel light. Once the car sets the code it goes into backup and runs great. Idles good and drives good. I have changed the ecu and the distributor from a known good car and still have the same problem. I have opened the ecu and tested the wires from inside the computer to the distributor. I have continuity and the correct voltage. I am stumped and now beginning to think that the code is something altogether different. Anybody with a clear head have any suggestions? I woud welcome and appreciate any suggestions. Thanks.