Every time after I rev the engine up to 5000rpm it then drops to around 500 & stalls, at idle. I replaced the stepper motor to no avail!
The car is an Evo 6 with a Evo 7 ECU, the car has no AC.
I thought to play with the 'Desired ISCV' tables, increasing steps @ high temps. Strangely, adjusting the ISCV tables had no effect on stepper behavior until I adjusted 'Desired ISCV' (with AC on)! even though the car has no AC, the ECU seems to think that the AC is on! I increased the steps to around 35 which kind of fixed the stalling issue but as a side effect, RPM got very erratic at idle.
I'm suspecting it might be an electric/wiring issue.

I'd appreciate your suggestions

 

I have no luck to make this fix(on euro evo8 or outlander) by adjusting iscv tables or afr on idle. Have a own thread about this somewhere here.
You have aftermaket inlet hose/pipe and blow off valve, right?
Basic things to be checked are if you have correctly adjusted idle screw on throttle body(if you modified target idle, you probably must adjust it to you new target? not the OEM¨values as in guide/manual, but also the desired steps on idle which you adjusted higher cannot correctly match target rpm, then some adaptation of ecu can take a place, but than can mess idle at cold i think)
And if blow off valve opening fast enought and closing before engine drop back to idle. Or any other leakage in hoses(make a leak test).

 

I have an aftermarket intake, but stock E9 (metal) BOV. I did replace the bov but it didn't fix the issue.
If I understood you correctly, I'd adjust iscv to fix the RPM drop & then adjust the idle screw to reach an acceptable idle rpm level... is that correct?

 

Actually, if your problem is just intake + bov(IX have stronger spring and bypass hole, so its opening differently than older plastic), then adjusting of iscv respective setting higher idle RPM just giving engine more strenght to be more stable, not fix of an issue.
About biss(idle screw) adjustment vs new idle target or iscv im not sure. Because idle srew is say as a constant for all idle tables. => i you set idle by screw too much, then you need less idle steps to reach target idle and vice versa. Unplug battery to clear all ecu adaptation, then warm up engine, by evoscan adjust idle screw according a guide and then log your actual iscv steps. Check it with iscv tables settings, adjust it if needed. And as i noted before, there is some adaptation in ecu, so after some time ecu will adjust it...by how much, it will tell you how much you have idle screw/desired idle steps or idle target is wrong.

Problem is reverse flow by MAF sensor by little surge from turbo when you closing throttle. Thats why older plastic bov is better than stronger metal one. And maybe IX maf is better to live with reverse flow(been told its different to older ones). Just for info, MAFs on 2000+ VAG cars, have noted in datasheet that can deal with reverseflow... it can surging like hell and no stalling.

 

And also check merlins evo tuning guide, on the end is topic about metal intake and maaf scalling adjustment when idle MAF Hz are not correct. You sayng idle is erratic, then it can be your problem.

I alwas have correct Hz, nice smooth idle and stalling as a bonus )

 

Is the IAC working properly? TPS adjusted properly?