Engine surging at fast idle

[WNowlan]

I started the truck today and let it warm up while I was checking on my daughters car. I noticed that is sounded like it was looping or surging after it jumped up to fast ilde. It was 21 out this morning the engine jumped up to high idle and then I noticed the sound from the exhaust. RPM gauge was not fluctuating. Is this normal?

 

[JCasper]

Mine does it, I have wondered about it, but not worried about it.

 

[CSkal]

Since it was cold out, maybe what you were noticing was the change in the sound of the engine as it gets alternately loaded and unloaded by the cycling of the grid heaters (greater demand on the alternator)?

 

[JCasper]

Since it was cold out, maybe what you were noticing was the change in the sound of the engine as it gets alternately loaded and unloaded by the cycling of the grid heaters (greater demand on the alternator)?

That's not the case on mine.



It will do it with a warm weather fast idle.

 

[Cattletrkr]

Since it was cold out, maybe what you were noticing was the change in the sound of the engine as it gets alternately loaded and unloaded by the cycling of the grid heaters (greater demand on the alternator)?

Grids should be off by the time the high idle kicks in.

Dad's '03 has done this for years. It was at the dealer earlier this week for that and a couple other things. No test turned up anything about the idle. It's bad enough you swear it's about to blow, but "nothing wrong".

I'm thinking about loading and unloading my smarty into it to see what that does.

 

[steved]

Mine had a slight bump in the high idle for over a year, then it got worse (to a full on lope) this past fall... an injector failed shortly thereafter.

This was a completely stock truck...

 

[CSkal]

Grids should be off by the time the high idle kicks in.

Are you sure? I know that on the rare occasion that I don't plug in, when the truck starts it runs up to 1100 RPM right away and the grids are still firing as normal.

Just curious.

 

[steved]

Are you sure? I know that on the rare occasion that I don't plug in, when the truck starts it runs up to 1100 RPM right away and the grids are still firing as normal.



Just curious.

You are correct...



If the truck is fired cold, and jumps right into fast idle, the grids continue to heat for their predetermined duration...



If the truck is fired after being plugged in, it will idle normally until the grids finish their predetermined cycle, then idle up...



I have never had the fast idle engage while the grids were cycling (after being plugged in)...

 

[hearingyourlies]

I've noticed this as well.



It is DISTINCTLY separate from the grid heaters cycling off. It sounds like a really aggressive cam in a big old V8.



I've heard injectors. I've heard normal.



Personally, as long as it breaks before my 100k mile engine warranty is up, I don't care.

 

[steved]

It is not normal... they should idle smoothly. As I stated, mine was caused by a failing injector... since the injectors were repaired, it is as smooth as glass.

 

[jltcasper3]

mine does it also, I have the smarty installed also, I don't think it did this until i installed some of the new updates to it. Mine sounds like it has an agressive cam in it, like a gasser. it just lopes at high idle sometimes dependant upon tempature. Who's does this that has a smarty installed?

 

[XXLTexan]

Mine does that too 35,000 on an 07' I have a smarty jr. Seems to do it in every setting including stock (0) It sound like a cam lope in a gasser. Makes me nervous=(

 

[RobertP]

replaceing the boost and the IAT sensor will fix this issue, at least it did on our trucks

 

[JCasper]

replaceing the boost and the IAT sensor will fix this issue, at least it did on our trucks

How much are these two parts and are they bothe easy to replace?