I have a 2001 Buick Century 3.1 l V6. My car drove fine and over the course of about 2 days it started becoming very sluggish when under load. It will idle fine. When we hook the scan tool to the vehicle it gave the code p0404 which comes up as EGR. It also threw a code for random misfire. I forgot to write that code down and do not recall what it is. Replaced EGR valve. Vehicle still has random misfire on all cylinders. The check engine light does not come on. Things that I have changed trying to find this misfire, plugs, EGR valve, wires, coil packs, ignition module, crank sensor, tested mass air flow sensor, tested cam sensor. We also checked fuel pressure and it was staying at 50 psi, we also put a dump on while it was idling and the vehicle did not sputter. The vehicle runs perfect when it's sitting at idle, when I put it in drive and try to give it gas it falls flat on its face, sputtering and missing very bad. We have blocked off the EGR valve and the mist did not get any better under load. When I unplug the EGR valve the car seems to accelerate better but is not running correctly. To eliminate the thought of bad gas, I drove the car until it was almost completely out of fuel, and I added STP fuel treatment, to clean the valves and remove moisture from the fuel if there was any, refilled with gas. This gas was purchased from a different gas station than the previous tank was. We also pumped out a test sample and let it settle on the workbench for a couple hours and there is no water in it. We have cut the front pipe in front of the catalytic converter to let the engine breathe better just in case the catalytic converter was clogged, and still are having issues.

2001 Buick Century custom 3.1 l V6 87,000 MI this is my own personal vehicle I have owned the car since it had 53,000 miles on it approximately 7 months, I've driven it to Florida and home into Chicago and home a couple times and have not had any issues with it until now.