Idle Fluctuation due to aftermarket intake?

[Galavoxx]

Installed the Weapon Research intake just last month and now I have this intermittent idle fluctuation. It doesn't happen all the time but the symptoms are always the same. After the car is warm, rpms will rise to 900-1000 rpms and then drop to around 700-650 rpms. This will continue to happen as long as the car sits at idle. I usually notice it when I pull up to a stop light. As I said, this doesn't happen all the time. Was wondering if anybody else has this issue with any of the other intakes or if this is a common problem? From my experience with motorcycle carburation, this symptom usually means that the idle jet is too big. Since this car is injected, I have no idea why it might be doing this. Seems like it happens more when it's humid outside but that could be my imagination. I also have a custom cat-back magnaflow exhaust. This could also be part of the issue.