05 6 speed problem. This truck is stock

When I am driving, starting and pulling loads everything is normal, but when I come to a stop the truck will jump from 500 to 800 rpm 3 to 5 times then sit right at 800 rpm.

But here is the strange part. the only time it will jump rpm is when the brake pedal is pressed.

When I come to a intersection and push my clutch in, put my trans in neutral, then release the clutch and coast the rpms sit right at 800.

Now when i come to a intersection push my clutch in put my trans in neutral, press the brake and release the clutch the engine jumps from 500 to 800 rpm several times then sits right at 800 rpm.

The engine will not change rpm when just sitting in the parking lot then pressing the brake pedal.

I have changed these variables with each test producing the same result
1)Hard acceleration prior to stopping
2)Light acceleration prior to stopping
3)Coasting in gear prior to stopping
4)A/C on or off
5)Trailer with electric brakes and no trailer
All have the same result.

I don't have drive-ability problems or fuel consumption problems

Sorry for going on and on but I was trying to give all the info I can.

 

So it only does it when you release the clutch in N?

 

Not necessarily, if I just push the clutch in and hold then push the brake pedal it will do it also, the brake pedal is the constant that activates the RPM variation.

 

Power steering pump may be going. What's the mileage on your truck?

 

72,xxx

I kinda thought it might be a hydro boost problem but the pump is quiet and operates well

 

Does it seem to take a lot of brake to get the truck to stop (like the engine were off, the truck was rolling, and you had to step on the brake really hard to get it to stop).

 

does it do it if you turn your headlights on?

 

The brakes work very well

---AutoMerged DoublePost---

With the headlights on or off the symptoms are the same.

 

I have more or less the exact same problem, and I've had it for the last few thousand miles. I'm not entirely sure what it is, but it seems like it could be rail pressure related. People generally describe their tachometers as "ratcheting down" from high rpms to lower rpms, stopping at 750-800. Mine basically drops like a stone as soon as I put the clutch in, braking or not, and bounces from about 500 to 650 to 850 to 600 to 750 and stabilizes there...eventually. ~5 seconds. No external factor seems to keep this from happening.

My current theory is that it's either a problem with the FCA or the CP3 overall. I'm in the process of deciding if the arson3 kit or the II Bag 'o parts is a good replacement for the stock parts.

 

As a follow up to this post, I just replaced the FCA on mine at 77K, and it seems to have solved the problem. The idle now ratchets down smoothly to about 800 and then stabilizes at ~750 without bouncing around.

FCA removal is: Unclip the wiring harness, remove 3 t-25 torx screws, and twist the old unit out.

Replacement came with allen head screws and was very simple to install, 30 mins.