Car problems please help
 

All my mods are in my sig. I have 72000 miles on the car. I've been driving with these mods for about 40000 miles with no problems until now. Had to replace coil packs as soon as i got it chipped but none since then.Drivin down the road one day was in fith gear doing about 75 hit the gas to pass a truck and car studdered bad check engine came on. Got the codes ran on it MAY sensor is bad. Also got some misfires from the spark plugs. Got all that done. Got the car back was idiling like crap soon as i turned and hit the gas bamb check engine light came on again. Pulled some more codes bad check valves. Got the car back again feels like she wants to pull like crazy now but is still studderin in second. Check engine light came on and flashed as i floored it but came off as soon as i let off the gas.Anyone have any idea what this could be. Bad gas maybe. I dont know shit about cars except Audi's are expensive to fix andI love mine so help me get it running right.
Matt