I'm new here, but not new to Impreza's. I'm the original owner of a 2002 WRX grocery getter! She's 60,000 miles young!
Within the past 5,000 miles I've begun the process of modifying her. Currently she runs tasty M1 TDT 5W-40 as of the last oil change, but unfortunately she was sipping M1 5W-30 for the rest of her life. I've religiously changed the oil every 3,000 to 3,500 miles. Within the last 5,000 I cleaned the MAF, changed the air filter, cleaned the IACV and replaced gasket, fuel filter, replaced cabin air filter, new plugs, drained and filled coolant...etc, so basically the maintenance is up to date.
Within the last 2,000ish miles I begun to modify her. GrimmSpeed thermal coated UP, Invidia catted DP, P&L Motorsports catback, some bushings, a boost gauge, GrimmSpeed Air/Oil Separator, and that's really all that comes to mind.
Ever since I did the UP about 1,000 miles ago I've had weird issues. First it started with being unable to reach peak boost of 13.5PSI; tracked this down to a leak in the UP (Seafoam into the IM vacuum line facing toward the front). The next day I started the car and heard loud rod knock. Literally out of nowhere, I went on to discover that the noise wasn't rod knock at all but rather a loose coilpack on the #3 cylinder. Torquing it down fixed all my issues.
Within the past two weeks my car has started to release white smoke from the passenger side area of the exhaust manifold, visible when I allow the car to warm up whilst I smoke my morning cigarette. In addition while idling at a stoplight white smoke will come out of the hood scoop and/or out of the passenger side tire area.
Yesterday I drove 200 miles to see my parents. Along the way I noticed sporadic puffs of white smoke that only seemed to get worse the further I drove. I'm not sure what to suspect other than a failing headgasket. I still see 13.5PSI of boost and have not noticed any loss in power.