I have a 2008 WRX with an exhaust, downpipe, intake, and tune that is having an issue with idling. The car drives fine and I don't notice an obvious loss of power when accelerating, but when I'm stopped at a stop-light, the RPMs will drop down to 400 or so and it feels like the car is about to stall (but it never has). Also, occasionally there will be smoke out the exhaust and it smells like a mixture of gas and oil. The other day I noticed a small amount of smoke coming out of the hood, so I pulled over and opened the hood to see the smoke coming from the turbo area (possibly turbo seals?). I took it to a shop the other day to have the spark plugs replaced and I asked them if they noticed any issues, the guy told me it was probably just "normal blowby for having 100,000 miles on it". Any help would be greatly appreciated.