Engine RPM Hunt at High Idle

[jltcasper3]

I have a question on something that just happened on my truck today for the first time. I went out this morning and startrd my truck to warm up, came back out ya know and it's in high idle because it's cold out, but i could hear and see on the rpm guage, a slight hunt up and down in the rpm (it's a real small hunt but is noticable), it does not do this at regular idle. It seems to run fine at cruising speeds, no hesitation. Has anybody experienced this before, and if you did what was the cause? I just hope it's not an injector going bad. I am going to change my fuel filter tomorrow and fill up, it's almost on empty. Any Input would help.

 

[Pawpaw]

Mine does it sometimes when its cold, but it will do it at normal idle speed too. It's sort of like someone is quickly revving the engine up about 50 RPM or so, about once per second.



I'm not talking about extreme cold either. It will do it when the temp only is in the 20's or 30's, but always after sitting all night.



Bob

 

[steved]

Mine just started loping this year... I almost attribute it to the fuel as one tank it will lope and the next it won't...

Sounds sorta cool, like it has a cam in it... I scanned mine several times and have not gotten any codes. And there has been no other detriments.

steved

 

[jltcasper3]

Well, i changed my fuel filter and filled up from a different place, it did not help. I loaded a different sw into my smarty and it still does it too, i have not tried returning to stock though.



Before a couple weeks ago it nerver did this. It is a real small rpm hunt only at high idle, maybe 10 rpm or so but you can hear it and see the needle slightly move. I can manually hold the throttle down with my foot at like the same rpm as high idle and it does not do it.



What else does high idle change that just giving her some throttle in park does not?



Has anybody experienced this before?

 

[TCuenca]

if its cold out its the grid heater cycling. . its normal dont worry

 

[DerekW]

I hate that stupid heater grid it is so frikin annoying and makes the truck sound like crap.

 

[TCuenca]

you rather have glow plugs than grid heaters??? i like the grid heater it makes everything less complicated

 

[steved]

As I stated, mine has been doing this "loping" since earlier this winter... I have no explaination other than fuel. It doesn't seem to affect anything else... my mileage and power are still the same.

steved

 

[Pawpaw]

No, it's not the grid heaters. I'm well aware of what my grid heaters do and they've never affected engine RPM.



Besides, grid heaters don't pulse on and off once a second.



Bob

 

[jltcasper3]

No it is not my grid heaters cycling. I went out this morning and it was not doing it but on my way home this afternoon after a 40 mile drive i got home put in in park and enabeled manual high idle and it was pulsing up and down slightly.

 

[propuller]

My new 07 does this also & it only has 2,000 miles on it. When the high idle engages it is more of a very rapid chug,chug,chug sound. That i cant duplicate with the throttle. It does it only on the high idle. I dont know if its normal maybe to help it warm up faster kinda like the 2nd gen 3 cylinder high idle.



Kurt

 

[Prairie Dog]

Could it be the A/C compressor cycling because you all have the defrost on?

 

[steved]

I dont know if its normal maybe to help it warm up faster kinda like the 2nd gen 3 cylinder high idle.



Kurt

Mine just started to do it one day (never had did it in the previous 2 years)... and it hasn't been to the dealer (or anyone else) for it to have been programmed to idle any differently. Unless they beamed the little DCX techs into my truck...



I still feel this is an external change, most likely fuel (LSD to ULSD)... but I can't find LSD around here to experiment.



steved

 

[jltcasper3]

no it is not the a. c compressor, air totally off.