2004 5.3L rough idle??

Ever since we had some cold weather my 2004 gmc sierra 5.3L started idleing rough, it seems to run fine when i'm driving its just when i'm parked or stopped it seems like it wants to die. This doesnt happen all the time some times it will idle fine and the engine light will go out. the diagnostic engine codes are p0131, O2 sensor low volts. p0171, system to lean. p0300 Random/multiple cylinder misfire detect. I think it may be the fuel pressure regulator according to some of the other post i've read can some one give me an idea where the fuel pressure regulator it is located on this make and modle truck. Any other suggestions would be helpful thanks

Confirm proper fuel pressure first, 60-65. Then suspect an o2 sensor issue possibly causing a lean mixture or a vacuum leak at or around the intake.

Ever since we had some cold weather my 2004 gmc sierra 5.3L started idleing rough, it seems to run fine when i'm driving its just when i'm parked or stopped it seems like it wants to die. This doesnt happen all the time some times it will idle fine and the engine light will go out. the diagnostic engine codes are p0131, O2 sensor low volts. p0171, system to lean. p0300 Random/multiple cylinder misfire detect. I think it may be the fuel pressure regulator according to some of the other post i've read can some one give me an idea where the fuel pressure regulator it is located on this make and modle truck. Any other suggestions would be helpful thanks

Took my truck in for same problem, they replace the O2 sensor, and its
fine now..

Same issue is happening with my truck. Everything identical. Have changed O2, spark plugs, spark plug wires, cleaned MAF sensor.
Cleared codes today, same codes came back.
P0300,P0171,P0131
Lean condition bank1 sec 1, random misfires,O2 input voltage low
Did anyone ever figure out the problem with this. Was it the fuel pressure regulator. Where is it located

The fuel pressure regulator is going to be on the fuel rail back towards the firewall. There should be a shrader valve on the fuel rail to allow you to check the pressure, but be sure to bleed the pressure off before you hook up a gauge so you do not start a fire. Either fuel pumps stop working all together or they drop off after they get hot. I honestly doubt it is the fuel pump. There are two TSB's on this, the first one states the element of the O2 snr cracks from water in the exhaust causing the condition (05-06-04-063), the second mentions intake manifold leaking air (05-06-04-029A)

all of these are faikure simple to check at home good luck

I forgot to tell you as well you should check the ground for the pcm to make sure it isnt corroded and the ground on the back of the pass. side cylinder head.