help!!! st205 keeps dying no matter what i do Options

[gt4joel]

hi all, ive had my jdm st205 for 3 years and I love her but shes breaking my heart. shes stalling for no reason. its been 4 months of diy research and replacing things.
anyone got any ideas cos im just about to give up.
ill run through the best I can whats going on.
the car will run great for around half an hour then a slight hesitation on throttle then 10 seconds later the engine light comes on,the revs drop to idle (900) and stays there ,
if I try to accelerate it will stall. it will start again but with difficulty, but still no acceleration, so have to turn it off and walk home swearing

the error code comes up 54. ive done all the forum research and know the symptoms\fixes. heres what ive done.
reconditioned the wta pump, checked relay, fine
water level fully topped up and sensor ok
replaced every water hose and vacuum hose with silicon.(pig of a job)
replaced water temp oil temp radiator temp sensors.
new rocker cover gaskets, fuel filter, air pod filter, dizzy,
changed fuel pump, changed fuel in tank, knock sensor done a year ago,
disassembled throttle body and cleaned aic and visually checked tps,
new oil and filter and fluids,


all I can think of now is a busted ecu because limp mode is supposed to get me home with half power but I can only idle.
and heres the kicker, next morning it starts up like theres nothing wrong!!
its driving me insane. and wanted to know if any one got any ideas.
I want my car back!! please can anyone help