At idle where is the timing corrections coming from in $OD? I have base SA set on 20deg in SA closed throttle table, base with est bypassed of 0*, base timing in constants of 0*. So why when the engine is running at idle I see the timing moving around anywhere from 16-22 deg. It appears that the ecm is applying some sort of spark correction based on idle error. If so, I dont see any place to make an adjustment.

 

That's likely exactly what it's doing. I know that in the $8D code there's two tables that address this. Idle spark advance vs idle speed error and idle spark retard vs idle speed error. The ECM will add or remove timing to help keep the idle speed stable. It looks like the $OD must have the same setup based on what you're describing. I actually have these tables set to zero, which ironically produces a more stable idle than the factory settings.

 

The PCM uses the spark and fuel as part of the closed loop idle control stratagy. There is a proportional spark routine that adds/removes spark based on how far away the engine is from the desired idle speed and the derivative routine adds/removes fuel based on how fast the idle speed is changing. It definatly works, but you have to make sure there is adiquate room for advance/retard in your closed throttle timing table if you choose to use these routines. If not, zero out the tables and it goes away. See the $0D hac I posted in "TBI guys, its time to update!". Its a bit dated, but it has those tables listed along with the associated address in the prom.