Hardly Stays Running

[MeanGreen03]

I just started my Tahoe up from sitting for about 4 months (started it up a few times with no issues). All I've done in that time period is put a system in it. Yesterday I started it up to drive and it is shaking and missing like crazy. I was low on fuel so I limped it to the gas station to get some fuel, thinking the fuel went bad from sitting. That didn't change anything. So went to Autozone to get the codes read and it came up with a P0300 (random misfire). This is what I've done up until now:
New Fuel
Fuel Additive
New Fuel Filter
New plugs and wires
Checked fuel pressure (50psi at idle)
Cleaned MAF, throttle body, PCV
Checked Coils (all are within a few ohms of each other)

I'm at a loss of what else to do and need to get it running pretty quick. As of now it isn't driveable. So any help from you techs would be really nice as I'm clueless right now. What I'm confused about is that it was running perfectly fine then it went straight into this mode.

 

[bkboatnsleds]

Not to sound dumb.. But could battery be weak? Seen bad battries do odd things!

 

[bahollis]

Never had that happen, but I looked up some info on that code-

http://www.obd-codes.com/p0300
http://www.engine-light-help.com/P0300-check-engine-light.html

 

[MeanGreen03]

Not to sound dumb.. But could battery be weak? Seen bad battries do odd things!

No, I charged the battery and even got it checked out at the parts store and they said it was good (not that those things are always correct).

---------- Post added at 10:05 PM ---------- Previous post was at 10:02 PM ----------

Never had that happen, but I looked up some info on that code-

http://www.obd-codes.com/p0300
http://www.engine-light-help.com/P0300-check-engine-light.html

Thanks, I checked those out. The only things I haven't done are the cats, burnt valves (which I highly doubt), PCM, cam position sensor, O2 sensor, and EGR (which mine doesn't have).

 

[ID_Escalade]

You might want to check your spark plug wires and make sure they are all on all the way. I had the same problem about a month after i put new plug wires on i guess i didnt put it on all the way

 

[MeanGreen03]

You might want to check your spark plug wires and make sure they are all on all the way. I had the same problem about a month after i put new plug wires on i guess i didnt put it on all the way

They're on all the way. i made sure they clicked on like they are suppose to.

 

[bahollis]

The only other thing I can think of is maybe the gas did go stale sitting there 4 months, and you have not been able to drive it enough to get the old gas out of the system. I have experienced crappy engine performance in my 94 Chevy back in the day, and it was gas bought at a Mom & Pop station in BFE. I'm not saying their gas had something wrong with it, but I'm sure they don't go thru as much as a name brand station so it prob sits longer underground. After that my next tank was Premium with an injector cleaner bottle additive, and it cleared up.

BH

 

[MeanGreen03]

The only other thing I can think of is maybe the gas did go stale sitting there 4 months, and you have not been able to drive it enough to get the old gas out of the system. I have experienced crappy engine performance in my 94 Chevy back in the day, and it was gas bought at a Mom & Pop station in BFE. I'm not saying their gas had something wrong with it, but I'm sure they don't go thru as much as a name brand station so it prob sits longer underground. After that my next tank was Premium with an injector cleaner bottle additive, and it cleared up.

BH

That's what I originally thought. I was practically on empty, as the light was on. I filled up with 22 gallons so that should have diluted it enough to not have an issue anymore. Maybe my injectors are clogged since it set so long all of the junk settled to the bottom and the pump sucked it up first. I would hope that the filter would have stopped it before it got to them though.

 

[afpj]

Having been lurking for awhile, the other thing that seems common that may cause your condition is vacuum leak intake manifold (gasket). I've had both intake manifold replaced (not just gasket...the big expensive PLASTIC manifold as well) and fuel injectors replaced at different times...both times had stumbling as you described, but I don't remember the codes. The links provided regarding p0300 seem to suggest these as possible culprits as well. Don't know if believe in Seafoam, but others do and it's cheaper than a new gasket or injector, although you could check injectors cheaply...just labor PITA. Good luck

 

[MeanGreen03]

I kind of ruled intake gaskets out due to no previous signs of them leaking (ie. rough on startup but when it warms up it goes away). Everything was perfectly fine, no issues what so ever. I'll try spraying carb cleaner around the intake and see what happens.