OK, just thought I'd share a recent tuning experience with you guys - with a view to saving somebody some frustration.
Vehicle was R32 Skyline mit RB20DET. Pretty basic job - bigger turbo, the usual FMIC and free flowing exhaust. Had Z32 AFM and 440cc GTR injectors fitted (with dropping resistors).
I'd fitted the NIStune board and programmed a base tune for the Z32/440 combo. Shop owner was complaining of general crankiness and billowing smoke when revved. Hmmmm.
Turned out they'd fitted a Malpassi rising rate FPR. Once that was binned it ran much better but while free-revving it still had a huge flat spot when throttle was opened suddenly.
We all scratched our heads - the others blaming the tune and me pointing at engine bay! In the end it was because a Z32 AFM (new) had been fitted without the air filter. Got a filter on there and it ran perfectly. Amazed looks all 'round.
Moral of the story: never underestimate the fickle nature of a Z32 AFM. Flow into and out of them is critical. Always tune with the pipe-work and air filter that will be used on the car in its final configuration.
PL
Weird running issues - no air filter
Moderator: Matt
Re: Weird running issues - no air filter
^ Needs to go into the tuning guide 
Re: Weird running issues - no air filter
There's actually been a note in the tuning guide under "Changing the Airflow Meter" for ages but I'll add some emphasis to the air filter bit.
"Tip: some AFM’s can be very touchy with respect to physical position. Z32 AFM’s can suffer badly if mounted too close to compressor inlets or if plumbing doesn’t promote smooth airflow in and out. Keep plumbing smooth, no sudden changes in diameter and with AFM as far as possible from turbo to prevent reversion effects. Try to use an air filter with a bell-mouth into the AFM. Problems manifest themselves as extreme richness and general bad manners at idle and low load. This is important and has the potential to cause huge tuning headaches."
PL
"Tip: some AFM’s can be very touchy with respect to physical position. Z32 AFM’s can suffer badly if mounted too close to compressor inlets or if plumbing doesn’t promote smooth airflow in and out. Keep plumbing smooth, no sudden changes in diameter and with AFM as far as possible from turbo to prevent reversion effects. Try to use an air filter with a bell-mouth into the AFM. Problems manifest themselves as extreme richness and general bad manners at idle and low load. This is important and has the potential to cause huge tuning headaches."
PL