I recently swapped a USDM H22A1 into my 4th gen Si, and I'm having one annoying little problem. The car starts up fine, cold idle is at ~1500, then it settles to around ~750 once warm---no problems there---but if you *blip* the throttle, the RPMs surge to 2000 before coming back down. Note, this *only* happens if I blip the throttle. If I lay on it steady, I have no trouble bringing it to 1200, 1500, whatever...but if I tap the gas slightly, the RPMs jump to 2000 before coming back down.

I've checked the throttle cable, and before I did the swap I cleaned out the TB and IACV completely, so I don't think those are causing the problem. I'm worried it might be a TPS issue, but won't know until I measure the voltage this weekend. I don't think it's a vacuum leak because idle quality is fine.

I've blocked off the EGR and Fast Idle Valve (with block-off plates; they're not on the motor), and I'm 99% sure I have a good seal on them. Could this problem be the result of air leaking in past the block off plates? I'll also go over my vacuum connections with a magnifying glass, but I really don't think that's it. Any suggestions? Obviously, this isn't a crippling problem, but it *is* annoying.