Is this normal VCT behavior?

[ttnuagmada]

Truck has a slightly rough idle, usually not that bad, but sometimes its worse than other times. Can't really find any consistency to it in terms of weather or whether the engine is warm/cold. no codes, dealer "can't find anything", no misfires, I run 93 octane, have used PEA injector cleaner etc etc blah blah blah. I have a 21 5.0 with about 27K miles on it. Haven't messed with changing plugs or anything like that, not to the point of throwing money at it just yet.

Was just playing around with Forscan the other day, and while im pretty sure it's nothing, I did notice that at idle, the VCT intake angles are offset by about 3 degrees. With any throttle they tighten back up, and otherwise track like they're supposed to while driving. I can't really find much of anything on what I should expect, or what's "normal", and I assume this is probably nothing, but just thought I'd see if anyone here had any thoughts on if this could be related, or otherwise just felt like info-dumping about the VCT system. Exhaust cams don't do this, they sit at like -0.2ish and never vary by more than a couple of tenths.

I have a tune, but I switched back to stock and cleared KAM and did the idle relearn, and it didn't make a difference.

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[Mosey]

I did not know an idle relearn was a thing.

 

[ttnuagmada]

I did not know an idle relearn was a thing.

 

[Reverberocket]

Truck has a slightly rough idle, usually not that bad, but sometimes its worse than other times. Can't really find any consistency to it in terms of weather or whether the engine is warm/cold. no codes, dealer "can't find anything", no misfires, I run 93 octane, have used PEA injector cleaner etc etc blah blah blah. I have a 21 5.0 with about 27K miles on it. Haven't messed with changing plugs or anything like that, not to the point of throwing money at it just yet.

Was just playing around with Forscan the other day, and while im pretty sure it's nothing, I did notice that at idle, the VCT intake angles are offset by about 3 degrees. With any throttle they tighten back up, and otherwise track like they're supposed to while driving. I can't really find much of anything on what I should expect, or what's "normal", and I assume this is probably nothing, but just thought I'd see if anyone here had any thoughts on if this could be related, or otherwise just felt like info-dumping about the VCT system. Exhaust cams don't do this, they sit at like -0.2ish and never vary by more than a couple of tenths.

I have a tune, but I switched back to stock and cleared KAM and did the idle relearn, and it didn't make a difference.

Interesting Forscan info. Do you take a lot of short trips? I think the 5.0's typically take several miles to get to the "cook the moisture out" oil temp. PCV valves aren't expensive. Maybe try a new one?

 

[FI300]

I have notice the same idle roughness on my 5.0. Its very random and no codes.

 

[blazef150]

Hm, my 22 5.0l is a little rough until it warms up. Then every now and then I get a stumble at idle when I have been driving over 40mph then come to a stop the stumble comes about 15 to 30 secs later.

 

[ttnuagmada]

Hm, my 22 5.0l is a little rough until it warms up. Then every now and then I get a stumble at idle when I have been driving over 40mph then come to a stop the stumble comes about 15 to 30 secs later.

I have something similar, though I wouldn't call it a stumble, it feels like maybe the transmission doing something a few seconds after i come to a stop. It does feel similar to the rough idle I've been feeling though, but it only lasts for a moment. Starting to wonder if all of it isn't just something the transmission is doing.

 

[jeffrt]

I get a similar random vibration on idle. Just recently started paying attention to the sensor that shows the amount of alcohol in the fuel. When I've gone over 10% (had a tank at 18%) I seem to get the rougher idle. If it's under 10%, it seems smooth. Only watched a handful of tanks though, so it's just a theory at this point.

 

[ttnuagmada]

I get a similar random vibration on idle. Just recently started paying attention to the sensor that shows the amount of alcohol in the fuel. When I've gone over 10% (had a tank at 18%) I seem to get the rougher idle. If it's under 10%, it seems smooth. Only watched a handful of tanks though, so it's just a theory at this point.

Mine has consistently been around 9.5ish

 

[FI300]

I occasionally run E85 in mine and have not notice a difference in the idle. It seems to do it occasionally with either fuel.

 

[ttnuagmada]

Nobody? I was watching it today and noticed that it seems like the angles separate slowly as the truck warms up. The duty cycle slowly increases on both as well. One thing I also noticed is that VCT_INT_DIF doesn't seem to show that it's happening. They still hover around 0.

 

[kezell17]

I have the same random rough idle when in neutral. Once I place it in any gear it goes away.
The rough idle is not consistant...it varies how rough at differnt times.

 

[jeffrt]

Just remembered that I disabled my auto start-stop a couple months ago too, and that really seemed to help smooth things out.

 

[ttnuagmada]

Just remembered that I disabled my auto start-stop a couple months ago too, and that really seemed to help smooth things out.

I've never had mine enabled. Turned off with either Forscan or a tune from day 1.

 

[ttnuagmada]

I have the same random rough idle when in neutral. Once I place it in any gear it goes away.
The rough idle is not consistant...it varies how rough at differnt times.

This describes mine for the most part. Can be felt in Park or Neutral, but is heavily subdued or undetectable when in gear. It's not consistent at all, sometimes it's barely there, and will kick up sporadically for a split second here or there, and sometimes it's bad enough that I've had passengers ask what my truck is doing.

I can feel it at more than just idle though. if I hold a rev at certain rpm ranges I can feel it there too, though mostly 2500 rpm or below. It honestly seems like something out-of-balance more than it does actual combustion issues.

I'm just struggling to tie it to anything. None of the accessories are wobbling, and the motor itself doesn't really look like it's shaking either.

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