I have a 93 Civic DX hatch. I swapped in a B18c1(OBD2), converted to OBD1. I get CEL # 3 only at 70% throttle or higher. I also get #21 after the #3 code kicks in. I know what the codes are, but why do they only come on at a certain RPM or throttle posistion? I have tried different MAP sensors and still have this problem. When this happens I can simply turn the car off, then back on and codes are cleared and the car runs good again. Has anyone ever had this happen to them?

 

Alot of times if u don't reset the ecu they come back on at random times, try first resetting ur ecu, if that doesn't work, and since u've tried diff map sensors I would check to make sure u got the wiring right, it's very very common that ppl when doing swaps will get the tps and map sensor connectors switched onto the wrong sensors, try switching them and see if that works. When I first did my swap I did this and it gave me code 3 then I realized I had the connectors on the wrong sensors, swapped em around and no more problem.