I installed my Apex WS exhaust this week with a test pipe, i ran into a minor problem with the O2 sensor but i finally got it in the test pipe, but now, ever since the exhaust has been on, when i first start the car and begin to move, in first and second gear it hesistates around 2 or 3000 rpms, like its coughing really quickly but quietly, like a low tone sputter, if i hit the gas harder it will eventually stop sputtering then accellerate as normal, after that initial sputter, it is fine for the rest of the trip...what can this be, maybe the O2 sensor not seated correctly? plugs wires ect? the only thing i can think of is it has something to do with the O2 sensor, other than that i dunno...any help or comments would be appreciated, thanx in advance

BTW...ever since i installed the exhaust 4 days ago the check engine light has gone on twice, but when i pull over and restart the car, it goes off...if that helps at all