my car doesn't idle too well. been tryin to fix that. anyway i had a broken wire on the o2 sensor so i replaced it, then i test drove the car in a snowstorm all seemed fine but i didn't drive far on account of the snow. brought the car back home and then couldn't get it started for like 5 days and brought it to the subaru place. They replaced the spark plugs and told me it is running rich. I'm on a custom tune from a reputable tuner and i've been driving around on that tune for a long time now. What happened and why is my car running rich now?