checking out an 05 today and its got a really rough idle sometimes and when you step the pedal down it kinda hangs at higher rpms for a couple seconds. bone stock truck, no power loss and no excessive smoke. any ideas?

 

I have one at the shop that is doing the same thing. I am changing the FCA tomorrow only because i have a new one on the shelf. i'll let you know how it goes

 

I have the same symptoms. What fixed it?

 

Most of the time when the rpm's hang for a couple seconds and then start coming down it's indicative of failing injectors. That was the tale-tell sign before mine starting doing the long starts.

 

Really easy to find the bad injector(s). All you need is an Ohm meter. Unplug the injector harness connections at the cylinder head (03-05 has 3). Setting the meter at it's lowest setting, gently probe the terminals. On a good injector, it should read between .4 and .7. Anything higher than .8, they need replaced.

 

As long as its the injector solenoid, that test will work. If it is anything in the mechnical internals of the injector, that will not show up. mine all ohm'd fine, but truck wouldnt run worth a poop. The RPM hang is due to injectors not closing correctly.
you need to have them flow tested to be sure.

 

Yes you said its bone stock, but also said your checking it out(used truck looking at buying or working on it?) sounds like the truck has/had a tunner on it... bro-inlaw same thing 05, removed the tunner and presto no more issues.
may have had a tunner/programmer on it at one time?

 

The rpm hang issue is mostly tuning related, the 07 5.9s have little hang(dodge fixed the issue in their programming). Although I still believe that it could be caused somewhat by a bad FCA, I would try that first.

 

My '03 never did it until the injectors started failing last year and I've had a programmer on it since '05.....just saying.

I wouldn't rule out the FCA though, but most of the time when it fails the engine will stumble and then proceed to race up on it's own due to ECM commanded fuel pressures.

 

Bad FCA is a possibility...


But injectors, depending on mileage could also be the culprit.. mine did the same, and would stick... when they gave out.. thus "hanging" as you said.... had three hang rpms for a little while, it only got worse.. then one day they hung open at 1500 rpms.. smoking white at startup.. and when revved up, would not come down.... and truck would bellow grey smoke... umm. yeah..

200K miles on original injectors... If you are on originals, and have no secondary 2 micron filtration.. even with a bone stock truck..... do not rule out injectors..

but lets start cheaper first.. FCA.... then worry bout injectors..

any dtc codes present?

 

This must be caused by injectors sticking and not sealing. When I first bought my 05 with 20k miles it would do it once in a while. Then I ran the gray bottle of Diesel Kleen Power Service and after the first fill up it stopped and has been trouble free since.

 

Ran Diesel Kleen through tanks and seems to have settled down. I only got the high RPM in neutral in park so not sure if I jumped the gun. My plan is to change the FCA and see how it goes. I also hear a little chirp that changes with the RPM of the engine and I suspect it is the lifters. Any thoughts?

 

I also forgot to mention that my gas mileage has improved from 18.5 to 22.5. WTH?

 

Why would my gas mileage improve?