I know this topic has been beaten to death but mine is a bit unique.

Just finished a professionally done LS/VTEC Swap b18/b16. Running mostly stock except for skunk2 intake/blox throttle body and plm header. P06 Chipped and modified ECU freshly dynoed and tuned. Plus OBD1 conversion. O2 sensor NOT installed and disabled/engine light disabled in tune.

Car ran perfect after tuning and parked it. Went to start it after a couple days and engine light comes back on (code 1 O2 content) and low idle at 750-500 or less and car will die. Now here’s the unique part, once the car warms up a bit by me keeping the rpm’s up manually and I restart it the engine light goes off and everything runs normal
Again. After that the car will
Continue to start and run normally for hours after until it totally cools down and the cycle repeats.

First thoughts were a bad ECU so it was fully serviced and capacitors replaced then tested under cold conditions and working fine. Same thing started happening again. All connections are good. Some sensors were used from my D15 and some are new. No other trouble shooting has been done yet.

Full disclosure - I’m new to this game and not a pro mechanic but am hoping for a DIY starting point that hopefully I can fix.
Appreciate your time and input folks.

 

Any suggestions out there for this or have I managed to stump everyone!?

 

Why would you not run a O2 sensor? Kind of important.. is your tune just running open loop reading pre programmed maps to not use the o2 sensor? Was it accidently a secondary O2 sensor disabled that is only reading how well the catalytic converter is performing but I think that's only for obd2.
Seems like it is getting stuck in closed loop trying to read sensors while warming up when it shouldn't but I'm no tuner or that good with electronics.. maybe test your coolant temp sensor at the ecu? I would just install a O2, get your tuner to activate it and cross your fingers? These are just ideas that came to mind to share after reading around.. I like to come on HT to pick my brain and learn or help with what I know.
Would like to learn a bit of this sort of trouble shooting myself.