Truck shakes a tiny little bit while idling. It is just barely noticable. I have a 2000 f150 5.4 4x4. I wanted to check on here if there was a common issue that would cause this before I started to look into it. Any ideas what this could be before I start looking? / should I be worried about it even? Like I said, it is very subtle and I have no noticed any other issues with the motor.. I do not think that it could be the IAC valve because it maintains constant RPMs around 700 while idling..

Edit: Replaced the plugs and wires today, and it still has the issue. Ideas? I have been told by a couple friends that this is normal and nothing to worry about, but I would like to get that confirmed/fix if I am able.

 

My 2000 f150 5.4 does that does too, its a very very slight vibration at idle, I started to research it, read about the torque converter slightly out of balance, build up or something, but i got side tracked with a different issue. You should try to reaseach that

 

How long has yours been doing it? / it won't affect anything else, will it? I don't really care that it does it, I just want to be able to fix it before it gets worse or effects something else or completely breaks something..

 

A sleight 'feel' of roughness is normal.
If the idle by the tach observation is solid there is no issue.
The PCM is constantly chasing the idle rpm and keeps correcting by modulating the IAC opening to keep the idle within +/- 50 rpm, as measured by the crank sensor reports back to the PCM.

 

yeah this is what is happening. The RPM stays exactly the same, but it feels like the idle is varying but when looking at the tach it doesn't change. I had a hunch that this was normal but just wanted to confirm. If I did decide to fix it, what would I look at?

The other guy who responded said to look at the torque converter, is this where to start? I'm not too worried about it since the 6 or 8 F150s I drove about 5 of them had the issue.

 

Unless there is a large vibration there is nothing to be done about it.
Even a carbed motor often does not idle perfect.
There are a lot of reasons for this.
The conditions for idle are not perfect everytime a cylinder is up to fire so the rotational torque will not be exactly the same resulting in a rotational torque difference.
The crank assembly weight, the converter assembly all act to smoothout (store inertia) the cylinder torque pulsations but some torque differences will still be present.
This is why the IAC is modulated to vary the air to 'counter' the rpm differences.
The OX senors look at the OX content and return a signal to vary the fuel injected in [the NEXT cylinder]to fire.. If there is any over or under correction, this will add to the differences in rotational torque as well.
But the overall corrections are very good in the design but still not absolutely perfect because there are to many small changes in conditions that can't be acounted for every revolution .
Then you have wear and changes in outside temperatures, fuel differences over time that the system tries to account for.
Unless there is a cylinder down on compression, a valve that does not seal etc, a missfire will be detected as a change in rotation time by the crank sensor for that cylinder when compaired to the average of the other 7 cylinders as stored in a software tables. This is a moving vairable value so the software can change the tables over the life of the motor to account for average wear overall and other factors.
I know it's a lot of info, but the system is designed to be very smart but still not perfect.
After all it's a full computer system controlling a big hunk of moving metal set in rubber mounts so it will move and not transmit to much vibration and noise to the chassis.
One could get into a lot of reasons the rotational torque will not stay the same for each revolutaion, so there is lot more to this yet.
Good luck.

 

My 98 F150 4.6 ltr has always had a slight miss at idle. I bought the truck new and it has done it right from the beginning. Never seems to change except maybe when it is cold in the winter months and this at high idle at startup.