Ok guys long time lurker first time poster here with a problem that has been driving me crazy for months now. Here's some info about the car, what it's doing and what's been done so far, any help is really appreciated.

Car is a 2000 wrx gc8, it had a 2.5 / 2.0 litre Frankenstein that broke and now I have swapped in an import EJ20. Car has front mount, Vf34, eboost2, 4.44 box and a few other things, only thing I'm 100% unsure of is fuel pump and injector size (been told jecs 550) fuel pump will be changed to walbro soon.

Now, after the new engine has been installed and tuned (making 170kw on 17psi) it threw a check engine light under half throttle, and has since done it at different points of driving, e.g heavy load, half throttle etc etc. It's broken down on me a few times under heavy load and to get the car started I released a fuel line from the filter, put it back on and presto, it drove again. Now the only consistency is that when I drive for 15 minutes or so, leave the car in the carpark for 10 minutes, then start it, it will throw the code, which will eventually got away. It doesn't throw it much under driving anymore, but always after it has been parked.

I have changed, maf sensor, pressure sensor, air flow sensor, o2 sensor, re routed air hose, cleared fault codes, turned my bov into pull reserc, and have had it sent to many mechanics who can't figure it out. Again and help / advice would be appreciated, I can leave more info if you need it. Thanks