I recently installed megan test pipes on my G35 (downpipe with cat removal) and the check engine light came on due to the O2 sensors being disconnected. However, when I started driving it and giving it a bit of gas/going up a hill and pressing the gas harder, the car began to shake back and forth a bit. I’m not sure if it’s because of the downpipe or if it’s something else that happened to occur at the same time I installed it, but I just want to make sure. I also took it back into the shop, no leaks or loose bolts, but there is a manufacturer specific code when scanned. Anyone know either the reason the car is shaking or the manufacturer code?