89 Honda Integra xsi check engine light trouble.
 

I just recently had a hydrogen fuel economy kit and computer idle adjustment removed from my car and now after driving about 5km the engine light will come on. If I let the car sit for a bit it will turn off and then another 5ishkms later it appears again. Anybody have a clue on what the issue could be or where the plug is for an auto mechanic if they want to do a computer engine check? cheers