I am starting to wonder about it.

My truck, if started and left unattended it will raise idle to 1000rpm (as supposed to) if temp is around 30s, then after few seconds, approx 20 or 30 idle will become different, a little rougher, and sound like looping a little, but not quite like a 3 cylinder shut down, which many swears it has been eliminated on 3rd gen trucks.

What this could be ? Injector timing changed by ECM to aid warmup ? INjection eventes modified to aid warmup ?
It is definitely a different idle pattern that I don't encounter any other time.

PS My truck runs great, excellent mileage and power and injectors have been tested twice by different dealers with no issues.

 

The CR's don't do a 3 cylinder high idle. From the scope readings I have seen it does split the main event in 2 when it goes into the high idle at low intake air temp.

That could be what is causing the rough idle if your injectors are not balanced or possibly carboned. Mine is dead smooth on the auto high idle and the idle up feature all the way to 1500 rpms. I would suspect a slight imbalance is causing the roughness.

 

^^^ I agree...

 

X3

Mine purrs like a kitten in auto-idle.

 

I agree with you as I have the same thing happening. It was about 4* yesterday AM when I started her up, she went to the high idle and I immediately noticed what you described. I switched the cruise on and manually set the high idle to 1K and it idled perfectly. Next time you have a cold start give it a try. Nothing wrong with my truck that I have ever noticed.

 

How do you do that. I didn't think our 4.5's had the high idle set feature.

 

You may need to have it activated at the dealership, but first try this.

1: Start truck
2: Turn cruise on
3: Hit Set (should climb to 1K if enabled)
4: use rt cruise button to + or- speed.

 

Mine idles just fine. High idles at all ranges just fine, smooth as silk. 65,000 miles. Smooth as silk.

 

Fired mine up today at 22* and all was good! Not sure what happened yesterday. I'm not worried about it though!

 

When mine goes into high idle it's rough, too. Smooth if I engage it myself. Been that way since new

 

i noticed if i have not ran it hard, it appears carbon on the injectors makes it idle rough.

if i romp on it that day, i will get a bit of smoke,

and it will idle smooth for a few days.

 

Two years ago someone stole my extention cord for my block heater and it was the wrong side of 30 below zero. I did not figure it would start but it did and in a few seconds it went into the 3 cyl mode and it sounded terrible (I thought it was a goner but there was lots of oil pressure ) I use synthetic 0-40 Esso motor oil. In a few minutes it settled down and started running on 6 cyl. That was about 50,000miles ago and I do oil sampling and although I would not recommend starting below -30 without plugging in I do not think I hurt anything but 3rd gens do have the 3 cyl cold start mode. (at least the 03s do)
Jim O

 

Nope, what you were hearing is just cold cylinders and the ECU adjusting the timing/injection. A cold start will make all kinds of noise and weird idling on any of these engines. Even the 12V's lope like crazy on a cold start.

 

It has to be a change in timing or injection events since it doesn't do it if I hold it at 1000 rpm manually.

Here's a video of the sound

http://www.youtube.com/watch?v=DfNMgLNTqzA

 

Mine does it too, I don't worry about it though. It is most likely just the computer changing things up, and they probably don't do it on the newer ones when the high idle is manually engaged because that is telling the computer you are using a pto and thats why it ramps it up. So since it thinks you are using a pto it wont change any settings that might mess with the engine speed while running that pto.