Engine stumbles as it returns to idle

[mikaelrules]

When the engine is revving from 3,000-ish rpm up and I put the car into neutral or disengage the clutch, the revs dip below idle (around 450-500rpm) and the car sort of "stumbles" and eventually catches itself again and the revs returns to smooth idle. I've already tried adjusting the blow-off valve to the point that there is already some compressor surge--and it seems to close quickly enough as the engine returns to idle, yet the stumble is still there.

Any ideas?

Btw, I'm running a Blitz DD BOV, Z32 MAF and PowerFC.

[stealthsr20]

are you reciculating your bov or open to atmosphere? if its open to atmosphere then that may be your problem.. your letting out metered air and the engine goes rich when you let off the throttle. My .02

[gotspins13]

did you check for boost leak?????????

[mikaelrules]

The BOV is currently venting to the atmosphere. I've heard that a blow off valve like that might cause it, but I have a couple of friends with the same setup without the same problem. Is there now way around adjusting it with an atmospheric BOV aside from going recirculating or with a blow through MAF?

gotspins13, Yup. No boost leaks.

[Def]

Are you running cams? Have you used Consult to find out what your IACV duty cycle is at a steady idle?

Try opening your IACV set screw some. Don't open it so much as to raise the idle, but to reduce the duty cycle at a steady idle.

I had a stumbling problem when returning to idle on my car after I put in cams(had the BOV both vented and recirc with the same effect). Turns out the stock ECU slowly ramps in the duty cycle on the IACV, and with cams your motor needs more air at idle. So you end up starving it as the ECU slowly gives it more idle air. Increasing the base IACV setting allows the engine to be happy with the ECUs slow idle air increase.

I'm not 100% sure if the PowerFC is the same, but try this and let us know if it helps things.