Hey there again! I understand your new to the forum so I'm guessing you bought your sti with these modifications on it?
It SOUNDS to me like you have a boost leak or a bad intercooler coupler (or one that needs to be tightened
Check all of your couplers and make sure that they are tight
Also, remember to check the boost lines around the turbo for breaks/tears
- There could be quite a few other things that could cause rough idle, Let us know what progress you make with checking for leaks