Oxygen sensor

[Mike McKown]

When an oxygen sensor gets fouled, is it likely or even possible it could intermittently throw the engine into open loop and then back to closed loop?

Can an oxygen sensor be cleaned?

[eurotiva]

IDK about the loop thing, but it can be cleaned with some brake parts cleaner

[blkfordsedan]

I don't think the ECU uses the O2 sensor feedback to determine loop status, just fuel mixture. I believe the open loop mode is based on engine temp sensor (cold start) and throttle position sensor (WOT). I could maybe see the ECU going into open loop and ignoring the feedback from the O2 if it's out of range, possibly as some kind of factory programmed "safe mode". I suppose it all depends on the particular engine management program. This is just my best guess.