Use a vacuum gauge to initially determine idle A/F while tuning the idle (initial) timing adjustment also. You want the highest steady vacuum using both adjustments. The front and rear throttle blades may also need adjustment. While juggling settings, the MAP will lower as vacuum increases. Later, you use the color of the outer half of the inner ceramic firing end and the O2% reading. O2% should settle close to zero at a steady fully warmed idle with the correct idle A/F. Idle A/F tends to be richer at idle due to slower runner speeds there. A camshaft design that also lowers power at idle (performance cam that increases power later in the RPM band) requires more fuel at idle. Most all engines need more fuel at idle to maintain more power at idle. With your extreme FI camshaft, you should be getting a MAP of 57-60 or less at 750. Something isn't tuned correctly. Your rear throttle blades may be opened too far at idle - this will prevent proper IAC control and will give a false adjustment correction setting. With everything set correctly, your fuel maps should correct to easily allow a lower idle. What you're describing happened to my 406 at idle - during my earlier tuning after changing to a single plane intake. The dual plane intake would never allow an idle below around 900 regardless. I had to keep the idle higher until the plug heat range, initial timing, and rear throttle blades were correctly adjusted with the new Vic Jr intake. I also had a third factor that happened during this time - bad fuel from a local gas station near my home. Once I replaced that fuel with fuel from a different station, I was able to quickly correct the plug heat range and adjust all settings for a smooth 750 idle in and out of gear - even as low as 700 without problem. Before that, I was getting all kinds of misleading readings that appeared to be what the engine wanted. If my other vehicles hadn't started running rougher than their usual smooth as silk, I might have overlooked the fuel as an issue. I had been buying most of my fuel from that nearby station for years without problem. I haven't bought fuel there again, and I haven't had any more fuel problems.