HI guys what would you say is the ideal afr on idle for a half bridge port 13b engine? Had a search around but can't find an answer
The answer is 'at the afr the engine likes!' Every engine is different so tune for the best idle, the afr is the afr and the value (for most purposes) is arbitrary at idle.
Ball park for 13.5 to get the idle stable and then tune around that the find the best idle you can.