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I’ve got a 2015 3.5 eco with 54k miles on it. Truck went to the dealer few months back for a rough idle and the dealer said it needed entire passenger bank of injectors. Since then it has had all new plugs gapped to .03 and cleaned the Map sensors on the intake. The injectors definitely improved it but I am still having a rough idle especially coming down from high idle. I know these trucks are known to have an occasional shake at idle but this seems more than what I have felt in other 3.5s. It’s been back to the dealer twice now and they can’t find anything wrong. I run FORScan on my 6.0 diesel so I decided to hook it up and start monitoring some things. My idle at warm bounces between 600-700 constantly without ever really settling down. But what really bothers me is my spark advance. When the truck is bouncing between idle points my spark advance goes from about 3 all the way to 15 and won’t find a steady advance point to stay. I’m also monitoring my MAP which is all over the place just like my idle and my advance. I still get 22mpg on the highway so it doesn’t seem to be affecting the mileage. Does anyone have what Ford considers acceptable MAP readings? Also I have read that it’s hard to say what the proper spark advance should be but is it normal for it to be so unsteady? I have tried premium and regular along with no ethanol all of which run the same.
 

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Start the truck and let it idle for 20 mins without touching anything, so it can complete the idle relearn procedure.
Some of these trucks do have a "rough" idle with really retarded timing advance.
 

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Discussion Starter #3
Tried the idle reset and got a little better idle now but still pretty rough. I know these trucks aren’t perfectly smooth but this just seems more than what’s normal. After the idle relearn my spark advance jumped between 7-12 instead of 0-12. Does anyone know if this kind of variation is normal? I would expect to see it stay somewhat constant with slight variations but not a constant 5 degree variation.
 

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Discussion Starter #5
Measured fuel trims below:

LT1: 2.34
LT2: -2.34

ST1: varies between -3.12 and -.78
ST2: varies between 0 and 2.34

Looking at the data I pulled from a 2 minute idle at operating temperature it seems the fuel trim changes lead the timing advance changes so I assume the fuel trim is what’s causing the spark advance flutter.
 

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Any way you can post the log?

Generally, when being read as a trim from Lambda, STFT and LTFT's should hopefully be around 1.0 (stoich) which is no correction. Usually you will have wiggle room of 3-5% which will settle on the LTFT trim and the STFT will be right on or about 1.0 constantly (after learning).

Your values seem to be in different units or I'm not sure what they are. If you had terrible fuel trims, I would expect to see something like .86, or 1.25. THe -3.12 and +2.34 are throwing me off. Maybe they are already converted to percent? But then what is the -.78...

Do you have any way to datalog and post the logs?

Spark will jump to counteract unstable idle. Add spark to bring idle up, dump spark to drop it. Map will flutter with this because the throttle will need to open and close slightly to control the air (IAC) which changes vacuum. You could have a sticky IAC, or a bad MAP (unlikely).

Log the following if you can

IAC or Idle Air Integrator
STFTs
LTFTs
Throttle Angle Actual
Spark Advance
Spark for Idle Control
Spark Source
MAP
 
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