So I got a 1998 Honda Civic EX Coupe MT which is meant to come with a D16Y8 vtec engine. Car wouldn’t rev past 5200-5500 and a code reader read p1259, which means there’s a vtec issue. Turns out the car had a D16Y7 non-vtec engine swapped into it at some point.

I Figured a D16Y7 ecu would fix my rev problem and get rid of my code so I could pass emissions.

I tried two different ecu’s for MT D16Y7 civics and both left me with a 300 idle, a drive that feels like that of a misfiring engine, and the code p1509, which means idle air control valve circuit failure.

When I put the original ECU back in I have none of those problems but then I can’t rev past ~5300 because the ECU wants to switch to vtec. And I can’t pass emissions with it because of the p1259 code.

I don’t know car electronics or ECUs very well so I’m hoping I just need to do something to make the ECU behave? idk please help 😅.

Below is a video of starting with the d16y7 ecu (37820-P2E-L32)
https://drive.google.com/file/d/1I0WGDJZwzC56FCT1EQtANuqJ0m2EftQk/view?usp=drivesdk