Hello I'm new here and have been reading through a lot of threads and can't seem to find anything on my issue but if I am missing something just let me know thanks.

For the problem I am having issues with my truck while IDLING, when you first crank the truck up it runs great and seems like there are no issues, but after it warms up a little bit or drive it around a few blocks and put it back into park or even neutral the trucks RPM's drop low like 400 to 550 low and the truck almost acts like its going to die. I have ran a Actron CP9125 pocket scan on it and have replaced 2 O2 sensors, a Output speed sensor, and the MAF sensor which cleared all the codes from the pocket scanner and I'm still having the same issue. I'm curious though too because I have been having a studdering issue between 40 and 60 mph that from what I have read that could be from a weak output of a coil if that could be causing the issue or not? I had the motor rebuilt 34k miles ago and the transmission was replaced about 17k miles ago and really like my truck but starting to lose my mind trying to figure out whats wrong with the darn thing. Any help is greatly appreciated!

 

NONE of those items will cause your idle quality issues. Wasted time and money...

Most common causes of your symptom:

1. Vacuum leak, especially in the PCV valve and its plumbing.
2. Sticky IAC valve. The onset of cold weather usually caused these to manifest.

Mild misfire. Usually cause by a COP and its spark plug. See if your scan tool will get you into the live data, the look at TID $53 to identify problem cylinder(s). Do NOT pi$$ away more money replacing all of the coils.

 

What is the easiest way to tell if I have a Vac leak? I can crank my truck up and listen under the hood and may be just the sound from being in my garage but I can't hear anything from apparent signs of what may sound like a VAC line sucking air from a leak?

 

Respectfully your not up on these computer controlled systems.
Clearing codes never fixes anything.
If there are codes, what are they?
You normally can't hear a vacuum leak unless it is a large one.
I detect two issues you have from your description.
One may be a faulty Intake Air Controller that may be sticking when hot from engine heat.
It may be stuck closed and can't control idle air.
Next there may be a faulty coil causing the studder on OD and light throttle.
The best way to find the cylinder with he faulty coil is to look at stored data in mode 6, test 53.
There you will find the record of misfire for all 8 cylinders.
One or more with high counts should be serviced.
Good luck.

 

No offense taken I liked vehicles better with out the computer systems! I do not have anymore codes, after replacing the parts I did codes cleared themselves. After removing the 2 o2 sensors I noticed bad places in them, so they were replaced the mass airflow sensor was full of dirt and cracked not sure how that happened but it was replaced instead of being cleaned, the output speed sensor was broken and know that one was most likely from these lovely corn fields in Iowa and hunting this year so it was replaced! Just kinda stumped thought that's what the computer system was for us to help solve motor issues along with other stuff lol. Will check on the coil issue tomorrow but is there a way to check the IAC without replacing it?

 

Crack the throttle slightly. If it idles smoothly, the IAC either isn't (sticky) doing or can't (vacuum leak) do its job. If you have a vacuum leak significant enough to affect idle quality, you usually have the corresponding "lean" codes.

You can try cleaning the IAC valve but the results are often mixed and are usually temporary anyway.

 

When the idle issue is present, remove the connector.
If idle does not change it is not controlling the idle.
Idle rpm is about 650 +/-50. Base idle is in the 500 range and set by throttle plate opening so never change that opening stop adjustment..
Often the IAC can be cleaned with spray cleaner until the cleaner runs out clean.
If you have not cleaned the inside of the throttle body, check that out. The throttle plate needs too be open a small amount to let a base amount of air in and also so the plate does not stick in the bore when the motor cools down.
Make sure the IAC slider valve inside is free to move.
This is how the air bypass is controlled.
If you find at starting the motor starts then stalls, the IAC has to be replaced because it still has a blockage but at a place you can't get to internally, to clean it.
.
Sounds like them corn stalk are beating the under side and the dust is very high so you need to account for that. Off road equipped trucks should have extra under shields from the factory.
Good luck.

 

ok so one issue solved and that's the studder between 45-60 had coil 3 & 6 were not functioning correctly replaced them and all is well there.

Now back to the idle issue. after replacing both coils I am now staying around 800 rpm in idle when rough idle kicks in, I pulled all the plugs checked the gaps and plugs for any bad places all look good, I then went on to let the motor warm up and wait for the rough idle to be present unplugged the IAC and motor instantly died out. Still took the IAC off cleaned the throttle body and the IAC until fluid came out clean and no change. But being winter here and nice and cold out I kept my garage closed most of the way and I'm starting to wonder if the EGR valve is bad I am smelling a strong raw fuel smell coming from the exhaust any thoughts on that? Can the EGR valve cause rough idle?

 

Idle is normally function of how much air passes by the throttle plate.
The IAC controls that amount from the pulses it gets from the computer to correct the idle speed to match a table in computer program to a +/- 50 rpm tolerance.
The normal idle rpm is 750 +/- 50.
It does this correction by looking at the crank sensor as a Tach signal.
The computer pulses the IAC open or closed until the crank signal matches the computer idle table within the limits.
Spark plug gap plays almost no part in idle in these systems.
What does play a part is cooling system temperatures via the CHT signal.
The IAT could affect the idle.
A vacuum leak could allow unaccounted for air to raise idle.
Also within the CHT and IAT functions the ignition timing is varied along with fuel injection amounts to match the air.
The above is the only way the system has to know what conditions to set up for cold starts and hot restarts.
Could EGR leakage affect idle? Sure thing because it upsets the air/fuel ratio as well as ignition timing.
Could fuel leakage raise idle? Not likely because this is a variable efficiency air engine and only needs fuel in small amounts to cause hot air expansion in the cylinders.
You need a Scanner to look at live data for some clues to the issue unless you get luck and hit the cause otherwise.



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