Just recently installed a Viggen Intercooler on my 1999 9-3 T5. However, the idle was blipping from about 1200 rpm to 2000 rpm and my check engine light came on right afterward. The idle has stabilized, but CEL is still on.
I've never heard of this problem, but try resetting your ECU. It may just be that the addition of the VIC threw off the ECU. Just disconnect the negative battery cable for 10-15 minutes, and make sure you have your Radio code