Usual suspects confirmation - slight engine shake at idle

[getdealtwith]

'04 Expedition with 2V 5.4 and 129K here, SoCal vehicle. I inherited ptetty fresh Denso plugs that are tight but I'm not sure how old the boots and coils are. Everything looks good, engine fires right up and pulls as it should.

I do get an irregular slight engine shake at idle. It feels more like unmeasured air than a misfire but being pretty new to the motor, I wanted to field a question here for those who have resolved slight engine shake (not proper rough idle or obvious misfiring): what are, in order or priority and cost (low to high), the most common culprits to look for?

For example:

1. PCV
2. Hoses
3. Coil boots
4. Injectors
5. Plugs
...

Thanks!

 

[Don Hall]

FROM A GOOGLE SEARCH - MAY HELP (?)

"Your Expedition 's engine creates vacuum when running. This vacuum is carefully controlled. If the vacuum system gets a leak, it will cause a shake when idle. A vacuum leak can be caused by a bad vacuum hose, intake manifold gasket, and other vacuum powered accessories."

I'm averse to using 'bad" as a fault condition. Bad is a condition of behavior.
My humble opinion is to use 'faulty' when referring to a problem.

 

[Transporter]

With the Triton engine and its COPs (Coil On Plug), moisture is your enemy. Have you checked your OBDII codes, IE has it thrown any Codes. If no codes, I would check for moisture. Pull the COPs and check to see if there is any moisture or condensation on or in the boots as this will cause arcs or misfires.

Also as a side note, with the EMC, they tend to idle at such a low RPM it is basically almost always a rough idle.

 

[TobyU]

I would start by looking at misfire counts on a scantool.

If you have none then go to the other ideas.

We had ONE (in hundreds) 4.6 Town Car with a slight shake in drive or reverse at idle.
You really couldn't feel it in park or while driving.
No misfires....even swapped COPS and plugs and injectors but never found it.

Dealer did cyl balance test and showed slightly low on two cyls.
Never did dig any deeper. Can't remember if I put a compression tester to it or not.
It was pristine cond with ow miles.

 

[getdealtwith]

Thanks guys. I'm not getting any codes for misfires. I'll start by spraying some starter fluid around the vacuum lines and this rubber elbow piece between engine and firewall that apparently likes to crack and develop leaks. The weather here is dry most of the year but if I don't find any vacuum leaks, I change the coil boots.

I'll share an update once I know more

 

[RichardH]

Good place to start, check the vacuum lines. I believe you should be getting a code if there was a leak though.

Not mentioned yet, but heard a while back that worn engine mounts can transmit vibrations when idling, but is smoother when driving.

 

[getdealtwith]

Good call. I'll look into those as well.

 

[Aspen03]

Good place to start, check the vacuum lines. I believe you should be getting a code if there was a leak though.

Not mentioned yet, but heard a while back that worn engine mounts can transmit vibrations when idling, but is smoother when driving.

I have the slightest of vibration at times when idling, engine runs great, no codes, noises, etc. Assumed it was mounts and planned to inspect when I do an oil change here in a couple weeks. I've had other vehicles exhibit similar behavior. I'm sure they are still present when driving bit it's so subtle you cant tell over the rest of the movement.

 

[RichardH]

I have the slightest of vibration at times when idling, engine runs great, no codes, noises, etc. Assumed it was mounts and planned to inspect when I do an oil change here in a couple weeks. I've had other vehicles exhibit similar behavior. I'm sure they are still present when driving bit it's so subtle you cant tell over the rest of the movement.

Yes sir. In addition to direct inspection of the mounts, on some previous cars/trucks I would prop the hood open, press on brake pedal and shift from Drive to Reverse, with just a little gas after in gear (lean on brake pedal and be safe please). More movement in the block when shifting (and goosing the gas) could point to worn engine, transmission mounts.

 

[Aspen03]

The GM L67/L32 are prone to mount failure and that method was a quick way to diagnose, aside from the motor sounding like it was bouncing off the firewall under heavy acceleration. Even w healthy mounts it could still move a bit. Poly mounts fixed it right up.

Are any poly options available for these?