JDM 3rd Gen 3SGTE Closed Loop Lean Misfire / Poor Idle, Engine Goes to Closed Loop EFI, it Coughs, Stumbles, and Misfires Options

[J3rkyBoy]

About 6-8 months ago, I installed an EBC solenoid for the already-wired in Greddy ProFec B Spec II in my ST205 front clip conversion (JDM 3SGTE, 3rd Gen, stock ECU) 1996 GT. During the week I had it in, it developed a misfire at idle (and a sputtering cutout between 2800-3100 RPM). The misfire appears to be as soon as it switches into closed-loop EFI mode and is as dramatic as someone flipping a switch: one second it is fine, and the next: cough, sputter, choke and AFR usually around 16-18 from 14.7. It is usually worse the hotter the engine is. It seems to be intermittent and can go a day or two without issue. As soon as I step on the gas and get it north of 3k it is typically fine and I'm good.

Please advise.

Aaron

[Bitter]

If you can't get live data from the O2 it's pretty trivial to probe it with a meter, though a graphing meter or an o-scope is best to use. Being able to see fuel trims and airflow sensor data would be good to.