It doesn't learn to a certain point, and then just stop there. It's a constant thing. I don't know about the 20 hp loss, though, that doesn't seem right. And if you are worried about your car being tame after the break in, just reset the ECU, and drive it hard, teach it who's the boss!

 

Your ECU constantly "learns" fuel trim over a wide range of operating conditions (blocks). The ECU (PCM,ECM) uses the O2 sensor feedback for fuel trim, it makes many smaller adjustments, then finally a big adjustment to get trim correct for each block. I won'get into it any deeper as I would have to look too much stuff up

I suppose you could be a little lean trimmed in certain blocks (operating conditions if you prefer) and lose some HP (run flat). But not for long. I am not sure hot rodding your WRX is a good way to try and "teach" the ECU anything since you would only be teaching certain blocks while beating the car. And WOT (wide open throttle) may be a set parameter as far as trim goes (I would have to go research).

To reset your trim strategies some makes offer the option on a scan tool, if not you can disconnect the battery and then touch the terminals together, this will drain the memory on most vehicles and make it use startup tables. The only time I would reset the trim strategies is after a tune-up that included a throttle/intake cleaning. Even then, the ECU/ECM/PCM should just adjust the trims over time so the reset is not really necessary, but I consider it kinda like a reboot, all computers need a reboot once in a while .

Jeremy "wrench" Crise
Jerry's Garage

 

I am not a modder, but I assume that all these straight pipe mods must come with ECM mods to take care of O2 sensor problems. Not sure how that can conform to EPA standards though . If you run around with your check engine light on, you probably are not at 100% performance, but I am not sure on Subaru's specific strategy.

By Hot rodding I meant beating your car to "teach" the ECM a thing or two. hehe