What would cause an inconsistent idle?

Sometimes it will idle a little high and then I can stop at the next light and it will be low, never stalling but it feels like it could, it does not matter if the A/C is on or not.

I adjusted the idle down after I turned in the fuel screw 3/4 turn to drop the idle back down and this is when I first noticed it.

First I thought it was the unusual cold weather we were having here in Southern California because this was only about the third or fourth time the grid heaters have ever cycled since I have had the truck, aside from the heaters cycling, could the KSB alter the idle speed?

But second thought now that it is in the 80's again it is still doing it.

I recently changed the fuel filter thinking it might be blocked and have a new fuel pump sitting in the garage to go in as a preventive measure.

I checked all of the linkage for binding and it all seems to be ok, the transmission also seems fine.

I have not really have had a chance to check it out but just trying to get some ideas first on what could be causing it.

The truck still runs fine other than the idle.

Also I really cannot see why some have such a problem with air when replacing the filter.

I installed it DRY, opened the bleed bolt, pumped the lever until fuel was squirting from the bolt into a rag, tightened the bleed bolt then after wiping up the mess turned it over.

I started and ran at a fast idle for a few minuets and it never had an issue with air in the fuel., it never even sputtered or skipped a beat.

Thanks in advance.

Jim

 

mine does the same thing sometimes...? now it won't even idle (something is plugged, or sucking air, or lp is toast)

I've heard this is a sign of a weak VE, but i don't know, mine still ran good when it did.

 

Change your gas cap.

 

I think Faith told me a long time ago that a weak ip could cause the idle to change but I am not 100% sure.

 

yeah I think my tank doesn't vent and that could be part of the problem because it makes a hissing sound sometimes when I open it.

So just get a new cap? does it need to be a dodge diesel cap or can it just be one with a vent in it?

 

We don't use gas here!

 

Mine does this too...I was wondering the same thing, does it need to be a vented cap?

 

Jim....I had the same symptoms when my other pump went south. I pulled the "out" bolt in the back of the pump and found metal in the screen. I kept driving until It would loose throttle and go to idle even while pushing the accelerator.
Do you know your fuel pressure going to the IP?

And the off topic guys.......No I do believe the sending unit in the tank has a vent. A quick fix would be to put a vented cap on then it will work fine. I don't know how your guys trucks are running. I've seen old 6.5 chevys suck the tank into a pancake.

 

It has been my experience that this often happens when first the fuel-screw is turned in, resulting in a bit faster idle, then the idle screw is backed off to compensate.

Myself, I would just put the idle screw back where it was; there is nothing wrong with a fast idle.

 

Unless you have an auto then a fast idle sucks when you drop it in gear.

 

I don't mind the fast idle, it makes my A/C colder at an idle and my alternator charging higher but it is the inconsistency that bugs me till I find out why.

I could pull the cover an check the sump for any metal fillings though I don't think I will find any, I always use Lucas Fuel Treatment with every fill-up, so it gets a healthy dose at least once usually twice a week.

The idle is not that high that it lurches froward when I put it in gear, just makes it much more nosier at the drive up window.

Jim

 

Where is this Out Bolt? is it at the restrictor in the return line?

 

When your truck is in the upright position shouldn't it be able to draw air through the anti-rollover valve above the tank?

Just a thought.

Jim

 

I think I also remember that from many years gone by.

Other than abuse and dry fuel with no lubrication what would cause the pump to self destruct, not including tampering with the pump head?

So what would make one pump last a million miles and another only last 400,000 if the only common ingredient is the diesel fuel?

Again just wondering.

Jim

 

Does it " hunt " for rpm's? Like rolling on the govenor?