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

[slavie]

The pulsing on the fuel line is probably normal. The pump is pumping, you're feeling the individual pumps.

As for your multimeter video, either the multimeter is not responding fast enough or the o2 is dropping out. No way to tell without a graphing function.

You're either gonna have to start investing in some tools and learning some more, or start throwing parts at it and hope something sticks. The latter is not ideal, of course, but many find themself in your situation.
You could try to bring it to a shop, but it's very, very hard to find a shop these days with a qualified tech that has the knowledge to diagnose anything, especially on an older car. Most shops these days just throw parts at the problem and never bother to diagnose.