Guys,
I did spend some time ensuring I posted this in the right place, if I'm wrong I apologize and I'll fix it.

I've got a 2002 S40, when running cold its fine everything works properly minus the exhaust smell, it smells like its burning rich. After its run for a bit and warmed up it begins to run oddly, the idle RPMs go from around 900 to around 400, if I run up on a red light and decelerate quickly it'll go dead. If it doesn't go dead and idles at around 400 RPM's when accelerating it drags as if it were flooded. The gas mileage isn't what it should be either.

New parts-
Spark Plugs
Coil Packs
Both O2 Sensors
Coolant Temp sensor

Taken off and cleaned parts-
MAS
EGR Valve

Also the codes Im linking were pulled prior to the O2 sensors, Spark Plugs and Coil Packs.
I also uploaded a pic of the old plugs and a pic of the car so you know its not the POS it would appear to be.

 

honestly your description sounds more or less exactly like what my car was doing, though I certainly wasn't getting so many codes; mostly I was just getting P0304, cylinder 4 misfire. When I'd first start it it would run ok for a little bit, but pretty soon the check engine light would start flashing and the performance would drop into the toilet. the idle would drop to 400rpm or less, it'd often just die. my understanding is that when the computer detects continuous misfiring, it shuts off fuel to the affected cylinder so if you were getting some power from that cylinder it's now gone.

for me all it took was new spark plugs and a new coil for #4, and it runs good again. you've already done that though. maybe a bad fuel injector?

 

From what I've been reading it seems like it may could be the Fuel Pressure Regulator, any thoughts? I'm about $50-$100 parts out haha. I knew from the start it'd be a relatively cheap fix if I guessed right and so far I haven't. It's getting pricey now. Thanks for the feedback.

 

Typical sign of a bad fuel pressure regulator is long cranking on cold start (ie to build pressure in the rail). quick test is pull the S vacuum tube off the bottom and check for any fuel drips. Have you looked for vacuum and intake leaks?

 

I have looked but I'll recheck, I wasn't really under the impression a simple vacuum leak could cause this. I did have the codes cleared and rechecked and now the only two showing are the MAP and MAF, reckon either of these could be a contributer?

 

When the fuel pressure regulator goes, it may not just be a vacuum leak. Gasoline may enter the vacuum section of the regulator and get sucked through the vacuum line. One test of the pressure regulator is by running the engine, turn it off, disconnect the vacuum line and see if gasoline comes out.