Chasing a P0300

[Newt Watson]

I am having the exact same issue with a 2005 2500 XL 6.0 4WD. The CEL will flash while idling and then will clear itself when truck is up to speed. P0300 and lean mixture code everytime. When truck is not idling, it runs like a champ. When idling it is bucking and missing. Cleaned MAF, newish throttle body (this cleared up a reduced performance error message), good plugs, wires, coils - those are not the problem. Maybe it is the MAF all of this time, looking forward to hearing from others on this issue.

It doesn't do it every time the engine is running, maybe 50% of the time. It is intermittent.

Ordered and took deliver in November 2004; 267,000 miles and still a solid truck.

 

[Mudsport96]

Id wager a guess at the crank sensor flaking out. Its good enough to run but "missing" where it is at some of the time.

 

[Fless]

Wouldn't hurt to swap in a known good MAF. Also, it could have a vacuum leak; have you checked the fuel trims at idle, and at 2000 rpm or so?

 

[Tonyrodz]

Wouldn't hurt to swap in a known good MAF. Also, it could have a vacuum leak; have you checked the fuel trims at idle, and at 2000 rpm or so?

Where exactly are vacuum lines on the LS motor? I looked really quick. Fuel regulator?

 

[exp500]

Anyone around Charleston SC with a Tech 2 to help out Cornelius?
I'm not at work to pull up manual, But I believe you are on to something= RE: unplugging MAF. I was thinking MAP. I'll look when I get a chance.

 

[Fless]

Where exactly are vacuum lines on the LS motor? I looked really quick. Fuel regulator?

I was thinking more like intake gaskets.

 

[Newt Watson]

I've checked for vacuum leaks and intake gaskets. That was my first thought on the issue. Have not looked at fuel trims. A bad MAF was the iissue with another vehicle I own last year. I will install a new one and update the forum.

 

[exp500]

If a vacuum leak, (manifold) then fuel trims should go hi- over 10 up to 30+. Maf wiring also connects to TB, so a bad ground/flexing wires on Maf plug. I'm sticking with MAP, thats where the cover bolts on so check wires there too. Pull it clean it oil gasket reinstall. and add a sensor in your scanner for it and monitor.
Even a bad pcv could be enough to miss. It's the 4 unconnected cylinders thats the stumper, not side by side.

 

[Newt Watson]

Update: I installed a new MAF and both upstream 02 sensors - truck runs like a champ now instead of a hobbled nag. Hope this info. helps someone in the future.

 

[Tonyrodz]

Update: I installed a new MAF and both upstream 02 sensors - truck runs like a champ now instead of a hobbled nag. Hope this info. helps someone in the future.

Did you ever get any codes O2 related?