I swapped a JDM F22B DOHC (JDM Prelude 92-96) into my 95 Accord LX not too long ago. It runs but is having some issues. When it's running in a low rpm range (just above idle speeds), the rpms surge back and forth making the car buck & shake. The car idles fine. It's throwing two CELs - one for the o2 sensor, and one for the ECT valve. It's at a local garage right now & the mechanic says he's tested the o2 & it had no problems. He doesn't think the problem is the ECT sensor either. I'm running the correct ECU for the JDM motor, the P39. I had him swap that out & try running my old motor's ecu, but that did nothing. It used to be throwing a code for the IACV/FITV, so I replaced the FITV & the cel went away, but the surging problem persists. The mechanic has double checked all the vacuum lines. I'd really appreciate any insight anybody might have into this problem.

 

And, as a little update, the guy has given it back to me because he's stumped. So I have the thing sitting in my driveway & can do some troubleshooting myself, so please if you have any ideas let me know. Or know of a really good mechanic around MA.

 

Is it really worth the trouble of hunting when for an answer when the ECU has already told you to replace the O2 sensor? I don't care what he tested. Replace that first and then come back.