I will check that with my tech2 and post ist later on

 

This is the reading right after I fire up the engine

Right after start

Right after start


And this is the freeze frame for P0101. But no MIL!

 

Engines idle fast after you just start them up. Let it warm up and enter closed loop fuel metering first

 

Here are the open loop readings at idle

 

You see how air flow is above what the computer "desires"
The idle air control position is also not what the computer wants.

Try cleaning out or replacing the IAC actuator.

 

Thx, good information.
Just for my understanding: MAF sensor and IAC airflow need to be the same?
I guess you mean the TPS sensor? The IAC is a module which you can't clean, just replace

 

No, definitely not.
OK, engine basics ...

MAF = Mass Air Flow
This is a sensor (heated resistive type) which measures and provides to the computer the total quantity of air coming into the engine. In your screenshots, it is being measured as grams (metric mass units) per second.
As a rough rule-of-thumb, the MAF metric value should end up being close to the digits of your engine displacement. You have a 6.0L engine. The idle MAF should read close to , and at least 6.0 grams per second.

IAC = Idle Air Control.
This is an aperture that the computer controls. There is a small air passage (bypassing the throttle plate) that lets just enough air into the engine for it to run while you're not on the accelerator pedal, and the computer is able to very precisely control the size of the opening (pintle valve) in this air passage (and also read back its position it seems). The computer monitors the engine speed (RPM) and adjusts the opening to get an appropriate engine speed ( which depends on things like engine temperature, oxygen sensor temperature, A/C status, electrical load, etc.). The units, in this case it looks like they're being called "counts", are arbitrary. The absolutely value doesn't really matter. The computer has no concept of what the numbers means. It simply adjusts up or down until it achieves the outcome (RPM) it is programmed for. Essentially trial and error.

You don't need to pay attention to the IAC value. What matters is the engine RPM at idle. (this is engine dependant. Mine likes around 700 RPM. Yours (a larger engine with more torque) is happy around 600 RPM. Tiny Japanese 4 cylinder engines need to run much faster to be feel smooth.

You can see from your data output the computer wants 550 RPM (RPM = engine revolutions per second), but it isn't getting it. It's close but a little high (570 RPM. too much).
It wants a smaller IAC position (32 count) but it is getting 37. (too much)
It's only hungry for 6.13 grams/second of air, but it's gulping down 7.03 g/s. (too much)
Long term fuel trim is positive 3% ... there's too much air in the mixture, and the computer is trying to add more fuel to compensate.
So you can see a trend here.


TPS = Throttle Position Sensor
Since you're idling, and not stepping on the accelerator, the throttle position is 0%. In other words: completely shut. Exactly what it should be.


The IAC constantly has air going through. It also has engine vapors going through it which have been recycled via the PCV system. The vapors are filthy. Full of exhaust, soot and combustion blow-by, raw fuel, moisture, vaporized oil, and other garbage evaporating from inside the crankcase. This (mostly carbon) can build up on the IAC valve and the results is unexpected operation and air flow. Also, like any moving part, the valve just wears out.

Yes, it can be cleaned. I've done it many times. Remove the throttle body and valve from the vehicle, get a can for brake cleaner, a tiny scraping tool, an old toothbrush, and other bristly implements, and go to town cleaning the valve and all the passages. If that doesn't help then just replace IAC valve which are not expensive.(you still need to clean the passages. Throttle bodies are very expensive.)

These vapors also settle in the throttle body and on the MAF sensor. This also confuses the computer, and reduces engine performance. It's a good idea to clean the throttle body, MAF sensor (research first) , and IAC all at the same time.

After cleaning or replacement, the computer will need a little time to readjust to it's new operating conditions. Looks like you have a Tech2 tool. You can trigger the relearn function yourself and speed up the process a bit.

Did that make any sense? Hopefully it aids in your troubleshooting.

 

Thx Joe! Great explanation
That helps me a lot and gives me a better understanding about whats going on
I will send an update if I have checked and cleaned all the part!

 

So what happens if the PCV valve goes out or fails how do you replace it do you have to place the whole valve cover or how would you address that situation?

 

Hi there! I recently had the misfortune of finding out the PCV valve is not serviceable and is attached to the valve cover on my 2017 Express 3500 With the cooler weather here in TX, I'm doing some preventative maintenance (coolant & brake fluid flush) and wanted to replace the PCV valve as well. Now that I know it's not a quick and inexpensive task, I'm online looking for recommendations on when to change a PCV valve, that's like mine and attached to the valve cover. Do you have any thoughts on when I should consider replacing the valve cover/PCV valve in my van? In general, I've seen recommendations to replace the PCV valve every 30k-50k miles, but that seems ridiculous when it involves changing a valve cover too. If it was just a $10 part and 10 minutes to change every 30k-50k, that would be easier to understand.

Below is more info in case it helps:
-the van runs like new.
-84,000 miles
-I've done the oil changes every 3000-5000 with Mobile 1 and since I bought the van with 21,000 miles. I switched to Amsoil for the last 20,000 miles of oil changes and will be using that going forward.
-I've never towed anything with the van.

Thank you for your time!

JD