2002 5.3 random misfire

[littlejimmy2003]

I have a 2002 z71. Since it has gotten colder when I start the truck (depending on the temp) the engine rpm will go to 2000 and then will start falling and then die. Didn't turn on the idiot light til this weekend and the code was p0300 which is random misfire. I would like any information on where to start or if anyone else has ever had this problem. So nobody has ever had this problem. After troubleshooting I have found 2 other codes 171 and 174 lean left bank and lean right bank. Cleaned maf sensor yerterday to see if that would help. One of the local guys said it might be fuel pressure regulator. Any feedback would be helpful.

[bojoe]

I have the exact same problem on a 03 suburban. I put plugs and wires in and cleaned the maf and then replaced the maf, sprayed either around the intake to rule out vac. leak and nothing has changed. I can't imagine both O2 sensors being bad. Mine starts and runs fine, just runs rough at an idle. I will let you know what I find if I get it figured out. Just don't want to have to take it to Chevy but if I have to I will. Going to FL for Christmas can't afford to have any let downs.

[bojoe]

To update my ongoing headache. I went to Chevy garage everything checked out fine except low fuel pressure. Changed filter = no difference, dropped fuel tank replaced fuel pump = no difference. Still missing and a random misfire code. Out $70.00 at Chevy and out $13.00 for a filter and out $280.00 for fuel pump. Runs great got 16.1 mpg on my 2000 mile trip to FL, just idles like crap. Chevy said it might be the intake manifold gaskets. Nothing is making any sense. I need to do something just don't know what if the intake gaskets don't do the trick.

[hvychve]

intake manifold gaskets are leaking...
I would put money on it. with lean codes both banks and random missfire codes, all the signs.
sometimes these are hard to detect, I use a smoke machine and when engine is cold, smoke machine shoots smoke into intake system and escapes where there is a leak, sometimes it takes a while to detect but very helpful , cold is important, because heat makes things expand and seal up and make it more difficult to detect.
with that said, if you have no smoke machine , try using propane, and on cold engine running at idle , crack the propane open with a nozzle directed at the intake and listen for stumble or rpm increase, if so you may have found your source, you can also use a can of carb spray, be conservative on the amount you spray, its flammable and its fumes can be picked up easily elsewhere , giving you the impression of detection.
I have changed many intake gaskets on these trucks for your exact symptoms, if memory serves me, injectors and intake comes off as one unit......There is an updated gasket for these trucks, so You will be better off asking for updated gasket , I would preffer dealer parts only, or if felpro can indicate update gasket, good luck, if im wrong, wont be the first time,

[WLPTMP]

yes there is a new style gasket i think its green