I have a 98' lude and made an OBDII to OBDI conversion but didn't use the harness and haven't had any problems since a few days ago. It all started when my car started to hesitate at around 3000 rpm then the CEL light came on. It threw 3 codes code 03, code 12 and code 21. I know the codes but the most rare part is that it works perfectly when the car has just been started but when I drive the car around for a couple of minutes it starts to hesitate at those RPM's. If anything like that has happened to anyone please let me know. The CEL lights now come constantly specially if I hit Vtec. Hope anyone can help.

 

Code 3: Manifold Absolute Pressure Signal
-High/Low signal
-Open or short in MAP sensor
-Map Sensor
-ECM/ECU

Code 12: EGR Valve Lift Sensor
-Lift Insifficient Detected
-High Voltage
-EGR Valve (with lift sensor)
-EGR Valve lift sensor circuit
-EGR control solenoid valve
-EGR control solenoid valve circuit
-EGR line
-ECM/ECU

 

Are you sure you threw a code 21?? I don't see anything about it

 

I'm pretty sure, I think the code 21 is " VTEC Solenoid Valve \\Open or short in VTEC solenoid valve circuit, defective VTEC solenoid valve" . I just don't know what happened because it just came out of nowhere.

 

Try reseting your ECU by taking off your negative battery wire off for awhile, then reconnect it. If the light comes back on, then you have a problem. The code for the VTEC solenoid is code 22 according to my resources...Go to http://www.hondaprelude.to/main_checkengine.html