I need to see if you guys might know why my truck is doing this before i take it to the dealer. It has just turned cold here this last week. well last week i had my trucks computer flashed from my old one av to ay. also after that i put my edge juice/attitude on my truck. well this morning it was around 91-20 degrees. So i set my high idle up to 1100-1200 degrees. my truck was idle just fine for less than a minute then the idle started going up and down 3-4 times.also noticed that my voltage Gage was jumping back and forth. Guessing from grid heater coming on and off.OK back to story after the frist 3-4 idle fluctuation's. The idle was fine for a little bit then started doing it again. so this time i turned the edge to (0) stock power with no change. so i just turned the high idle off and let the truck idle stock for one minute. truck ran great and drove it to work with no problems.the only thing i have done emission delete wise is unplug my egr. which i have not had anyproblems with everyday driving. so i do not know if i might have aproblem with my edge box or my truck or if something is wrong with my AY flash. also for got to say that after the ay flash somethimes it seems like my exhaust brake does not come on. SO does anybody have a clue about any of this or am i just screwed??? thanks Mopar72

 

My stock truck does the same thing when it is cold and grid heater is kicking on / off. RPM flucs and voltage flucs as well...

 

Some guys were having this issue on cold startups after unplugging their EGRs. They would blow lots of white smoke too and it was not the typical white smoke you might see on a cold morning. Once the truck was warmed up then it would be fine the rest of the day though. Mine did this too a couple times. I simply unhooked both batteries for about a half hour. I then hooked them back up and I always wait for the 5 dings to complete before I start the truck. I have not had one more issue with this in over 4000 miles......

 

It has just turned cold here in Alberta - well not too cold yet. My cold start observations: (The truck is an April 2008 build - engine built March 28, 2008)
The only mod is the EGR is unplugged.

below 0 degrees C (32F) with the block heater not plugged in the truck starts and instantly goes into high idle at 1100 RPM. I don't touch any pedals, I just turn the key and start the truck. I can engage the exhaust brake and it comes on at this engine speed. When the grid heaters cycle, the idle drops about 50 RPM for a milisecond and returns to 1100 RPM. It reminds me of engaging the Horton fan on my 97. This repeats itself as the grid heaters cycle. No wild idle fluctuations though. If I touch the brake pedal, the high idle comes off and I must manually use the cruise control to bring the high idle back on or wait the 1 minute??? for the automatic high idle to turn on again. There is no abnormal behaviour or smoke, it's just a little louder than when warmed up.

Today was -16C and I had the block heater plugged in for 2 hours. The truck started and did not go to automatic high idle as the coolant temp was too warm. I engaged the cruise and set the high idle to 1100 RPM and turned on the exhaust brake. As the grid heaters cycle, the same behaviour as described above occurs (slight drop when the heaters cycle on then back to a steady 1100 RPM idle).

 

evidently the high idle WILL work even having the block heater plugged in , it all depends on the ambient temp's.
if it's below 15 the high idle will kick in with an engine that's warm during an extended idle,but it takes a few minutes
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Well I don't have a 6.7 but I have the same issue with my 5.9... What I have determined is that the fuel is cold and thick. The FCA can't properly regulate the amount of fuel needed (when it is thick)... So it is opening and closing more than it should, instead of staying at a steady postion and this will cause the truck to idle like that.

If you do a search on DIY FCA mods on the CR 5.9 forums, you will see guys having the same issue when they mod the FCA and don't remove all the burrs on it (but thiers acts this way all the time, not just during cold) don't ask me how I know ...

I doubt you are really going to have any issues with this, and I have come to think that its just something that adds character to the truck...

I am guessing this is what you truck sounds like (this one is VERY exaggerated and on a chevy)...

http://www.youtube.com/watch?v=X15ikCZ-IpE