Surging RPM after engine is warm
 

I have a problem similar to a post by "North Pole Hooker" back in Nov2011. The only exception is my truck only does it when warm.

When I start my truck and it is cold, it idles and runs smooth. I do notice a very pronounced lope when at high
Idle 1000rpm. It drives just fine too.

However, when engine temp gets above 140, this is where the problems start. If the truck is in park and I rev it to 2500 or 3000 rpm it comes down a bit, stops, comes down a
bit more, then finally makes it down to idle. Also when highway driving and I let off the accelerator to coast, the rpms are choppy when slowing down. Seems to have a slight knock ( louder than normal) when warm too. Doesn't do this at all when cold (less than 140F). I have no white smoke at startup and it starts right up, even after sitting for 8 or 9 days. EGTs are normal and fuel mileage is decent (around 18 to 19 MPG empty highway, hand calculated).

I just purchased this truck a few months ago and it has always done it. I wasn't too concerned because I got a good deal. The truck has 173k miles and appears to be bone stock. I installed an Edge Juice with attitude to monitor temps and pressures. One thing that concerns me is the previous owner used a FRAM fuel filter. I don't know for how long. I am leaning toward injectors, but I want to be absolutely sure before I fork out the money. Any thoughts from the pros would be greatly appreciated.

If you're out there North Pole Hooker, what resolved your
Buddy's problem?

Think I would start with a injector return test and graphing the desired vs actual rail pressure, this will give you a idea of the health of the injectors and fca. What percentage is the fca at while at idle?

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Update:
I pulled injectors and 1, 3 and 4 had tons of carbon buildup. 4 had 1 - 2 mm thick coating of carbon around the top of the injector. 1 and 3 had chunks at the top, maybe only 1mm thick. 2, 5 and 6 had minimal carbon buildup inbetween the copper washer and the nozzle. I ordered the new style injectors and new feed tubes. Ouch! I also ordered the dual cat fuel filter setup.

How do I clean the excess carbon buildup from combustion chambers 1, 3 and 4? Spray a little water, with a squirt bottle, in the turbo inlet while at 2000 rpm and let the steam clean out the carbon? Wait until I have a heavy load and run the crap out of it? Any suggestions for a combustion chamber cleaner that isn't snake oil?

Why order all the new parts? The Carbon you see is pretty typical but could be caused by an injector not atomizer correctly. I wouldn't do anything to clean the upper end. Drive the truck once reassembled and you'll be good. The key is to make sure the injector seat area is clean! Don't know that I would be confident enough with the little data provided to condemn a set of $330.00 injectors!

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My injectors are original with 178,000 on them, so new injectors and connector tubes, not feed tubes. Oops. The fuel filter setup is to protect my investment. I have been burned in the past with crappy fuel from a high volume truck stop. I had to drop the tank on my isuzu turbo pup and there was sand in the tank! Yikes. Cost me a set of injectors. They were cheap. One dodge injector is about the same price as all 4 on that truck. Thanks for the response.

Same thing is now happining to me
 

What did you find to be the fix to this problem? My Cummins is a 2006