S14 SR: Bogging at 2.5K rpm, boost is fine

[TFD]

Hi guys, I need some more ideas from you;

Problem:
After swapping in DW 740's/Z32 MAF/GT2871/JWT ecu, the cars stutters and bogs at part throttle (around 2.5 - 3K rpm) and vacuum is low (0.6is bar). After kicking the throttle it will boost like a mofo and everything seems fine. With previous stock setup everything ran fine.

Checks:
Boostleak - No, checked
Vacuum: Took entire intake apart/cleaned/new hoses etc.
O2 sensor - weird readings, seems allways lean and doesnt fluctuate up and down like it should. When disconnected the problem is still there.
Plugs: Black as the night
MAF: Seems to work well according datascan and cleaned it recently.
IACV: Works according datascan and cleaned recently.

At datascan there are no codes. When putting in timing modes to check timing and adjust low idle, the car allmost wants to stall. Adjusting the idlescrew has no effect on idle.

BUT: When I up the enginetemp (with datascan) with as little as 2 degrees, the car seems to take of (1500rpm or so...).

Now I bought a (US) JWT ecu for my UK SR20DET... can there be a problem with wrong tempsensors of o2 sensors?

And how can I check for vacuum leaks when everything is on?

Sorry for the long story but something is defently off the scale here.

Thanx!

[PyR0NiAk]

Long stories are appreciated. It shows you're actually trying to fix the problem instead of have us tell you what's wrong with minimal details. The 2.5 - 3k issue typically comes with maf problems. If you can, borrow someone else's and see if maybe the MAF is starting to fail. The fact that your O2 sensor says it's lean when your plugs are black kind of gets my attention, though. I've honestly never heard of issues with JDM (No such thing as a US SR20DET ECU) ECUs being used in UK cars, but I've also never read that it works. I really don't see what would be different, unless the JDM ECU is for an S13 instead of an S14... The most common way to check for vacuum leaks is to start spraying carb cleaner in suspect areas. If the idle changes when you do it, you have a leak there.