Hi i'm new to cars, so bear with me as I try to describe my problem lol , I just recently sold my first car and bought a 2003 Mitsubishi Lancer OZ Rally. Now, when i bought it, the CEL was on, and I asked them what the problem was. He said it was some kinda oxygen leak because of the gas cap not being screwed on tight enough, and he said he'd fixed the problem and cleared the CEL, which he did. 2 days later, the cars light came back on and i noticed a really loud noise coming from the car....it's an exhaust leak, i can see about a half inch gap in the piping near the headers, so i at least know that's a problem that needs to be fixed, but that's not why i'm posting. Whenever i'm driving and accelerating it sounds fine (minus the annoying exhaust leak sound) but whenever i remove my foot from the pedal it feels as if the cars shaking just a little, it doesn't matter what gear i'm in. To add to the problem, whenever it does this, it sounds as if it's backfiring or something, again, knew to dealing with/fixing cars, so idk if this is a problem, but the backfiring sounds like it's coming from in front of me (as if to say it was freakin backfiring from the gap in my exhaust pipes). My uncle's hooked it up to a little machine that's supposed to tell why the CEL is on, and it came up with "Engine too lean", which it said is another affect of the exhaust leak. please help, and if you need other information that i may have forgotten to give ask and i'll try to figure out how best to answer. I'd really like to understand my car and cars in general and any help would be greatly appreciated. thanks