Loss of accel and sputtering when driven a little

[Haase]

Alright guys, once again thanks for all the help in my previous questions, but i have one more. After i worked out the oil problems with my turbo I finally got my little 420a running well, however after I let it warm up and i drive it for a while, like 8 minutes or so, it starts sputtering/sounding like a lawnmower and starts to run badly and i have almost no acceleration untill I really stomp on it and i start running boost through. I do have a loud exhaust leak around my downpipe area, but i cant seem to find one at the manifold, also, could it be a bad O2 sensor causing this? those are the only two ideas i can come up with and i plan on fixing them both but any input helps, thanks again

 

[GRAVEDIGGER]

Pull your spark plugs and have a look at them. They can tell you alot, like if the car is running rich/lean or misfiring. If your exhaust leak is before the o2 sensor that COULD cause a false lean condition, so check that out as well. Good luck.