E38 Idle goes into Open Loop for a few seconds, strange commanded AFR

[rao]

I noticed recently that my e38 car (15 Chevy SS Manual) does something unusual when it is at idle.

If it is at idle for more than a minute r so, such as when at a stop light, it will go into open loop with a rich commanded afr for about 5 seconds then it commands a lean afr for a few seconds then it goes back into closed loop with a normal commanded afr.

Any idea what is going on here? It is always in similar conditions and always for roughly the same period of time.

I included a snippet from a log showing the behavior.

Not a big problem, but I'd like to know why it is doing this.

[5FDP]

I want to guess at a possible cat converter test??

Is that someone you can log?

[Mep_q8]

It does look like the COT enrichment coming. You can see Catalytic temperature drop from 710*C down to and also you Intake Valve temp. Post your file lets take a look if this is active.

[rao]

Good thought, COT threshold is over 1700 F, not anywhere near the temps being seen.

The search continues.

[SSUte01]

It's a cat test like mentioned above based on the info you provided and without seeing it first hand. You can disable it under Engine Diagnostics.

[schpenxel]

I'd disable it and see what happens. Engine diag-->exhaust, disable catalyst test and post O2 test if you have both options.

[rao]

That appeared to do the trick. I need to check if this affects the readiness monitors.