ok so here is my situation hopefully someone has something helpful. i traded in my 03 WRX for an 06 STi. but the STi i currently have was modded by someone else.(might i mention if you traded in a black STi with gold rims and it said precision tuning on the windshield in lakewood new jersey you are an absolute moron and need to stick with old muscle cars that don't mind being rigged in ways that don't make sense.) mods include an APS front mount intercooler and cold air intake, perrin turbo inlet, 3 inch down pipe, and a manual boost controller. i do not have a check engine light on but i am getting some rough idling and some bogging down, stuttering, or chugging whatever you want to call it but on the freeway cruising it is incredibly annoying. i changed the pcv valve and it seemed to have fixed my gas mileage problem and the car ran very smooth for about a day but is now actually acting up worse than before much more defined. anyone that has had this problem fixed would be a great help. i had a z24 cavalier that did this once and the coil packs were the problem but i don't know if i can part with 240-400 dollars on an educated guess before i ask other people.