look closely for any leaks after the meter and before the t.b.
i don't think your issue is a blow through draw through issue. but you have alot of couplers and connections after the meter that can screw up the mass air meter reading. meter should typically be 0.6-0.8 at idle, check that first. very lean idle can cause what you are having which could be caused by a leak or a bad meter.
check all your piping 1st. blow off or bypass? if blowoff, is it leaking at idle? then borrow a meter from a friend.
1.how does a lean at idle cause black sooted plug's?
black plugs = rich condition ,lean = very white, possibly burned off plug straps
2. rob are you using a drawthrough or blowthrough meter?
im just curious
3. this is comon knowledge, if you use a open atmosphere BOV with a drawthrough meter, you will encounter a highly rich conditon under closed throttle coming out of boost due to the engine not actually recieving the metered air , which could cause stalling, fouling plug's ,rough idle, stumbling ect,
A CBV (by-pass valve) must be used as being a closed system, any loss of air for which fuel has already been metered by the movement of the airflow sensor plate, will result in an over-rich condition and possible backfire
. A CBV is found on many "OEM" original engine manufactured EFI turbo systems.
A BOV(open atmosphere) is suited to an EFI system that uses a blowthrough mass air meter that meters air right before the throttle body or a MAP (manifold absolute pressure) sensor. As the MAP sensor source is inside the inlet manifold's plenum chamber, relieving air before this with a closed throttle butterfly (throttle lift-off) will not affect running.
but there are diffrent strokes for diffrent folk's
i hope this help's