EGR issues?
 

I have a 2003 LS. It just recently started running real sluggish. It loses a lot of power going up hill. So bad that I have the accelerator to the floor and my speed is going down! It's to dangerous to drive to a mechanic. The check engine light came on and we pulled "PO404" from it. I took the EGR out and looked okay, but I went and got a new to replace it. It still runs sluggish. I have also replaced the fuel filter, the air filter and cleaned the mass air. The car has a 165K. Any ideas?

How old is your catalytic converter?, they often get plugged in our cars and cause problems such as this. One way is to start the car and let it run for a short period and then look under the car to see if it is extremely hot, please don't touch with your hands lol.

DTC P0404 Exhaust Gas Recirculation (EGR) Open Position Performance

So you are on the right track with the EGR valve. Mine went last year and same sort of scenario as what you are describing.

I would first start by checking all the vacuum lines in and around the EGR valve, as well as replacing the gasket if you didn't do so. There is also the rare chance that you got a bad replacement, although it doesn't happen often nowadays it still does happen, so if you still have receipt wouldn't hurt to take it back for a replacement.

Usually when it is the catalytic converter like I mentioned it will throw a code, but not always which is why I still suggest taking a look under the car to see if it is overheating when running.

I would then check to make sure all the plugs are in good shape, as well as the wires, if you aren't running on all cylinders this will cause a lot of the problems you are describing, but then again I believe nowadays your computer will throw a code if it is the plugs and wires, but still better safe than sorry, just make sure they are all connected properly and not loosened off from the caps that connect to the plugs, or where they connect to the coils, sometimes moisture in the coil will also cause an issue like this.

Then there is also the possibility of water in the gas, wouldn't hurt to throw a bottle of gas cleaner/water remover in your tank just to be on the safe side as well.

Sadly when trying to track down a problem like this, where you have changed the part the computer is telling you is bad and the problem still exists it makes it hard. You have the option of going to a GM dealer and getting a deep scan done on your engine's computer, but this will cost you, with the handheld scanners they are not always completely accurate with diagnosing, but generally give you a good direction on where to start.

Keep us posted on your progress

The EGR valve gets a signal from the PCM telling it to open or close the pintle. That signal is dependent upon signals received by the PCM from the TPS, MAP and Coolant Temp sensors. You may want to check those circuits also for loose/dirty connections - especially the coolant sensor.

So, I loosened up the cat from the headers to see if that would allow it to breath more and go. As it turns out, the cat is in fact stopped up. Now I know what to fix. I appreciate all of y'alls help. It's always good to bounce ideas off of multiple people within the MC community.