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BOVs get pulled open by vaccum, creating an intake of unmetered air, leading to lumpy idle and stalling (unless idle is set high) when coming to a halt.
There are 3 ways to clear the problem:
1/ use map + iat instead of MAF (long, expensive, not worth it)
2/ recirc the BOV (cheap, efficient, only "downside": no more wooosh sound)
3/ remove the BOV (needs blocking off the BOV hole on the piping)
If you can easily try 2 or 3, by all means try. I don't think it will solve all the problems here, but at least it will remove one of the list.
The ECU tries to adapt AFR with the closed loop system, but it does not change timing. It will change timing if the engine is near stall, which might be what you are noticing. Timing changes your idle speed. The ECU has an internal target idle rpm, you should adjust this and set the IACV to match that idle. Of course, you can change the IACV setting to match the idle you want without changing the target idle in the ECU, but then the ECU may start doing weird things, like considering it is too high and pulling timing to get it lower, then adding timing because it is near stall.
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