Cummins ISX Rough Idle - Idle Adjustment

[KatieLady]

Could someone give us advice on RPM's at idle on a Cummins ISX?

KW is idling at 500 RPMs and is extremely rough.

Is this normal? I thought it was at 600 and it seems to have changed by itself?...is this possible?...why?

Also.... how could we do an low idle adjustment? ...

Thanks! ...HELP...it is driving my husband crazy...I am not sure it is really that big of a problem....but we just bought this truck and he is freaking out over the rough idle ...

k

100 RPM drop sounds like an injector not working.

[Kranky]

100 RPM drop sounds like an injector not working.

Actually, even with a problem such as that which causes a misfire on 1 cylinder, the ECM will still keep the engine idle at it's set speed, although the engine will run rough.

Is this normal? I thought it was at 600 and it seems to have changed by itself?...is this possible?...

I know there is a procedure on a Mack whereby you can reset the engine idle speed within a range from 500 to 750 RPM, in order to get a smoother idle.
It is:
Vehicle stationary with parking brake on.
Accelerator NOT pressed.
Turn speed control on/off switch on and off 3 times within 2 seconds.
Depress and hold accelerator to desired idle speed.
Depress and release the set switch
Release accelerator.
Depress and release clutch pedal.

The new speed is now locked in the ECM as the new idle speed.

Check the Cummins owners manual, there is probably a way to do this on your engine too.

[allan5oh]

Is there a way to check codes?

I'm stabbing in the dark here, but I think he needs to check the crank sensor.

[Kranky]

I'm stabbing in the dark here, but I think he needs to check the crank sensor.

If there was a problem with the crank sensor wouldn't the engine be running poorly throughout the RPM range???

I agree that it should be checked for codes.

[allan5oh]

No, my dads detroit did that exact thing.

Changed the sensor, it was fine.

[KatieLady]

Doesnt crank sensor tell when to fire?...how would that relate?...

We might try resetting first....ummm...we will get back to you... thanks SO much... we will talk about it...

k

[allan5oh]

It might "scatter" at idle, and be fine at higher revs. Maybe it's loose, I don't know.

Have you called cummins yet?

Have you pulled any codes?

[KatieLady]

Appreciate all the feedback...just thought it might be a simple quick fix..

what may be loose?

thanks,k

[allan5oh]

crank sensor. I have no idea where it would be on your truck.

[Orangetxguy]

Could someone give us advice on RPM's at idle on a Cummins ISX?

KW is idling at 500 RPMs and is extremely rough.

Is this normal? I thought it was at 600 and it seems to have changed by itself?...is this possible?...why?

Also.... how could we do an low idle adjustment? ...

Thanks! ...HELP...it is driving my husband crazy...I am not sure it is really that big of a problem....but we just bought this truck and he is freaking out over the rough idle ...

k

Is it possible that someone bumped down on the cruise control set-resume switch, while the main cruise switch was in the OFF position?

If you haven't already paid a mechanic to look at it, start the truck up, turn the Main Cruise switch to the OFF position, then "Bump" up (or set) on the "set-resume" switch. This should give you a 50 rpm upward adjustment on the idle. Normal idle for the cummins isx should be 650 rpm.

BOL

[MoonShine Steel]

Could someone give us advice on RPM's at idle on a Cummins ISX?

KW is idling at 500 RPMs and is extremely rough.

Is this normal? I thought it was at 600 and it seems to have changed by itself?...is this possible?...why?

Also.... how could we do an low idle adjustment? ...

Thanks! ...HELP...it is driving my husband crazy...I am not sure it is really that big of a problem....but we just bought this truck and he is freaking out over the rough idle ...

k

Is it possible that someone bumped down on the cruise control set-resume switch, while the main cruise switch was in the OFF position?

If you haven't already paid a mechanic to look at it, start the truck up, turn the Main Cruise switch to the OFF position, then "Bump" up (or set) on the "set-resume" switch. This should give you a 50 rpm upward adjustment on the idle. Normal idle for the cummins isx should be 650 rpm.

BOL

Stan...you da man. I've trucked for a lot of years but always able to learn new things. I am a recent Cummins ISX convert from the yellow motor crowd after a couple turbos fell off, push rods, etc (all under warranty but who can deal with the downtime from such sloppy quality control out of Peoria lately?). I've owned Cummins stuff over the years and lost my infatuation with the beige engines with the STC and low-flow cooling days thus I found the enjoyment of the old 425 B-model CATs, eventually ending up with a new C-16 600 horse in 2000 that was the beginning of my dislike of the CAT brand.

Idle speed on this ISX 565 has been low since day one and being new to this overhead cam business, I had no idea what was the norm. After a while however, I realized it was idling too low (the engine data plate says between 580 and 620 RPM is the deal for this engine). I hate to let it idle..I won't...but I operate a PTO-driven hydraulic system on my portable parking lot, so I do the "Cruise On" then hit the "Set" switch on the bottom side of that toggle to get the PTO feature and the R's come up to about 800-850 when I am loading.

Long story short...searching Yahoo for ISX idle info, I found CAD and your reply right here about the possibility of the cruise being bumped down...I didn't have a clue about trying that. That was exactly what had happened to my truck either at the factory or at the dealer and the dealer didn't share anything at all about something like how the Cruise switches work and I felt no need to ask cause how difficult could that be??? I never tried the cruise switch in the Off position and bump the set switch cause I figured nothing would work if the main cruise switch was set to Off. I figured wrong. The Set switch will change the idle RPMs even in the Off position. Needless to say...I tried what you said and it fixed the low idle on mine. I was about to schedule a look-see at Cummins for this and some other parameter changes but you took care of the idle.





So...Thanks for sharing. You never know how far your informative posts will reach I guess. Now if I could find someone well versed in the Cummins INSPEC software and the Road Relay 4 info.