Mattis for your problem i'd be checking the heater hoses as mine cracked and slowly leaked caused big problems its hard to get to but check the 2 hose connections beneath the iac valve
I cannot recommend them highly enough. Way home from work gave it a little stick even with boost dropping to 15.7psi ( my boost controller ) its incredible.
R33 gtst - mod list
Hybrid fmic
Hks super dragger 3.5"
Splitfires
Nismo 740cc inj
Stock cat (made into decat)
3" stainless intake
Z32 AFM
3A racing pod filter
Apexi evc
Plugs are bcpr6es gapped at 0.8
Tune in progess 2 hrs to go.