Engine shakes and surges in neutral at 3000 rpm

[napierjohn]

This site has been a great resource for me so thanks guys.
I have an engine issue I'm hoping a wrench turner or two around here could help me resolve. My 2004 4.0 4WD with 145,000 miles has a strange engine issue. I don't often rev my engine too high but found recently when I rev the engine in neutral it starts to shake around 2800 rpms and gets into a surging mode at 3000 rpms. Under load, though, the truck drives great, even when I hit it hard. It isn't throwing any codes.

My question is: What is the behavior of the engine when it reaches the 3000 rpm rev limit? Could the surging just be the effect of the rev limiter?

I have ruled out some reasons for surging in neutral and so far I have
- checked for vacuum leaks
- cleaned not to dirty ERG valve
- checked the spark plug wire connections
- used a small scan tool and can see at 2000 rpms in neutral the O2 sensor oscillates in range, short fuel trims hover +/- 2%, and long fuel trims are low, too.
- read fuel pressure at 50 psi though spec is 60-65.

If the rev limiter isn't making the surges, I suspect the fuel pump but don't want to jump to conclusions.

Thanks in advance guys.

 

[Ed Fenwick]

John, there is a rev limiter for park and neutral so the young folks don't rev it and then drop into gear. I don't know what RPM it is set to but I remember when I first bought the truck that it would stumble in neutral. Maybe bigger wrenches can offer better advice.
God bless Ed

 

[DILLARD000]

Yep the rev limiter. Just not good to rev it anyway. At 145kMiles OxSensors are overdue for a change too.

 

[napierjohn]

So does the rev limiter mechanism make the engine surge at 3000 rpms?