I have done a swap on a ek civic ....a eudm 1.4is to a d15b 3 stage vtec and ai have a problem with the idle
The problem is electrical .... not mechanical after some diagnosing.

The engine harness is am original RHD ...converted to LHD ....so to suit the chasis .

The problem is that according to the HONDASH datalogging the ect sensor has erattic reading .. it varies +/- 10 degrees
I changed the ECT sensor with a new one just to eliminate it from the equation... with the same result!
So the simptoms are as followed:
- the first time i start the engine it wil have a very high idle (like 2000 rpm) wich after somedine gows down slowly to 1200 but never under ...even it the engine gase warmed up...
- if i shut of the engine ...and then start it up again it will idle at lower than 1000 rpm ....and now the vtec (wild cam ) is working...
- after sometine (never the same period) if i shut of the engine ...and then start it up again it will idle at lower than 900 rpm ....and now the vtec-e(econo)and vtec (wild cam ) both are working...

The Discovery i made is: If with the engine on and worm i disconect the ECT conector from the sensor the idle goes right under 900 rpm..and i dont get a CEL
if i plug a volt meter to the conector ...and measure the voltage doesn go steadyb to 5 v ...but it oscilates ftom 3 to 5 v

so how dows the ecu engine termperature sensor circuitry works .... cus i think it is somthing from the ecu.
The ecu is the one it came wit the engine is a manual p2j-003 ecu.

Excuse my poor english ...
and could someone enlighen me about what chould be the isue in the ecu?

 

the ECT (coolant temp sensor) is powered from the ECU internally, it is connected from C13(signal) to C22(ground).
that source voltage is from the ECU's internal 5V rail, if that is oscillating as you describe, you either have a flakey connection at C13, a bad solder joint in the ECU, a bad part internally, or a bad ECU.
hopefully the ECUs 5V regulator is not moving around like that or the ECU will never work right. (monitor C19 to check)

 

An air bubble in the cooling system will cause erratic ECT readings. Though I think that once 180 F or so is reached, the ECU considers the engine warmed up and does not change the idle speed further.

Make sure your thermostat is the proper temperature and is good.

If you have two wire IACV (EACV), unplug it and confirm the idle drops to lower than normal (400-500 rpm). If it idles fast with the IACV unplugged, you have too much air going into the intake somehow, and the ECU will not be able to keep it from idling fast.