Rough idle and fluctuations

Alright I am super confused and have been trying to find the culprit of this for a while.
I have read through dozens of threads similar to this but seem to be unable to find a definitive answer.

Problem:
Fluctuating and rough idle.
The idle on my 5vzfe goes from 700 up to 850, then back do wn... up... and so on.
When the idle is high, it is slightly rough, not crazy shaking but it is noticeable.

I have so far done the following (both because of this issue as well as getting this gal up on maintenance):
- Spark plugs & Wires
- Replaced vacuum hoses and tested for leaks
- Cleaned the IAC (then replaced a month later after nothing changed)
- Replaced the Throttle position sensor
- Tried another throttle body from a scrapyard
- MAF brand new, then cleaned again*
- Fuel filter new (within 5k miles, 3 months)*
- PCV Valve and tube also brand new. *

*updated original post with these
Here is a graph of the RPMs over a few minutes. Data taken from an OBD2 while running at idle.

Any potential solutions are welcomed and any references to other threads and solutions welcome as well.

Thank you all

*edited to add complete list

 

Weird. MAF? Fuel filter? Maybe even PCV valve?

 

Good reminder thank you.
MAF brand new, then cleaned again
Fuel filter new (within 5k miles, 3 months)
PCV Valve and tube also brand new.

*updated original post with these

 

Have you reset ECU after your list of changes by simply disconnecting and reconnecting battery then driving it for a day or so to reprogram?

 

What are the fuel trims?
What do the AF/O2 sensor do when this is happening?
What does the ECT temp read?
Does the truck ever make it to CL? Or does it stay on OL?

 

@boshak I did do this each time, for a few days. Been dealing with this since Oct '22

@TnShooter I have added this chart showing fuel trims.
Coolant temp was reading at steady 87-88*C

Has never had a CL for this issue

I will have to do a re run and check if my OBD2 has o2 / af sensors (this is oxygen and what else?)

 

OL and CL are Open Loop and Closed Loop.
With those coolant temps you are most likely in CL.
Long term trims are high.

What scan tool are using?
I like the graphing it provides.

 

Maybe try a new igniter https://www.ebay.com/itm/122423992566

 

@TnShooter I am using bluedriver scan tool.
What would cause the high fuel trims without throwing a code?

@Steves104x4 Thanks for the idea ill check into this!

 

Have you run Seafoam or Berrymans (or really any other fuel cleaner) through it and done an Italian tune up? Throw a heavy dose of cleaner in the tank and drive it fast on the highway.

 

@goingplacesanddoingstuff I did use a seafoam can on a half tank of gas before departing for a 2k mile road trip. Was going in the 70's the whole time and filled up a few times. Used 2 seafoams over ~6 tanks.

 

A vacuum leak can cause high fuel trims and rough idle.
Does the truck run fin while driving it?

 

Tricky vac leaks can be pcv hose/valve, brake booster, evap canister....

 

Do you have the AC on? Those pulses look synchronous with the compressor clutch

 

@TnShooter I checked for vac leaks by spraying carb cleaner around and listening to engine, as well as putting a gauge on a few of the vac lines. Cant seem to find a leak.
It does run completely normal when driving it, problem only at idle.

@O'Silver_Taco Any tips for detecting one of these tricky leaks?

@treyus30 I dont remember exactly ill have to test it with ac on/off. Curious, if the ac is on and causing this, why so frequently and why would it make it rough? I never would have thought to check the ac components.
Will run another test tonight with/without AC.

 

A smoke machine is the best way to check for vac leaks....

I'm getting a vac code......when I pull that hose off from the canister to intake...
engine stumbles like that real bad.....sometimes dies....

That brake booster leak is rare.....but happens...

That pcv system is prone to leaking both at the grommets on the older ones.....and the hose...
the gas fumes eat all that up....cause rubber and plastic to swell....


Little smoke machines that use some external air source start at about $70 and up
run on baby oil and car battery....

 

That shows it cycles about every 18 seconds. The AC compressor doesn't run at 100% duty cycle otherwise it would overcharge the liquid side (you have pressure sensors on the lines). The IAC is supposed to raise your RPMs when it turns on, and lower it when it's off. What you're experiencing could be completely normal. If it shakes a lot, your engine mounts may be bad

 

@O'Silver_Taco
So I didnt have a smoke machine but I had a cigar....
From my redneck science experiment tonight I was unable to locate any leaks.
I do have a coworker who possesses one of those fancy machines and Ill be able to borrow next week to verify.


@treyus30
Alright so you got me really curious and I repeated the test. It looks like it only fluctuates like that when the ac is on. Without it, idled for 10 minutes, no fluctuations or rough/shake.
I inspected the AC components and the belt was a tad loose so I tightened it a little and resulted in the following:

A significant change from original


Decided to tighten it a little more:


Got me feeling pretty dumb here lol.

So, I understand your explanation about the duty cycle causing the fluctuations.
Side note: this is the ONLY difference I have been able to make so it seems like this is the correct path. (all other part replacements resulted in the same graph as the initial post, no changes)

I do not understand the part about the rough idle though. I initially thought engine mounts too but why would it only be rough when the AC is on?
It is fine at idle with no AC, as well as driving.

With the AC on, it is rough, but if I give it just a liiiiiitle bit of gas, it settles down and does not shake at all.

 

Low RPM creates the lowest frequency oscillation. It can move more in one direction before switching, so you get the biggest feedback. AC on = more load = greater amplitude. Higher RPM is higher frequency so the mounts dont have to work as hard

 

@treyus30
Interesting, that makes sense. Is there any definitive way to check for bad motor mounts?
Only thing I see is to try to give it gas with the brake engaged but seems difficult to do with a clutch lol.