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?

 

[RichardH]

I did a little digging, and came up w/ these folks:

https://prothane.com/wp-content/uploads/2017/12/PROTHANE-Catalog-12_4_17.pdf

Never used them but could be a starting point. States they have poly mounts... engine and body

 

[getdealtwith]

OK, so I thought I'd circle back here to report that I found that the vent line from the driver side valve cover wasn't plugged into the elbow piece right at the valve cover. The random shaking is 80% better now but not completely gone yet. I'll replace the pretty rotted hose along the firewall next and will check the motor mounts as well. Thanks for the support everyone!

 

[TobyU]

OK, so I thought I'd circle back here to report that I found that the vent line from the driver side valve cover wasn't plugged into the elbow piece right at the valve cover. The random shaking is 80% better now but not completely gone yet. I'll replace the pretty rotted hose along the firewall next and will check the motor mounts as well. Thanks for the support everyone!

So that was a pretty big vacuum leak. A good way to hear those is to take a 4 ft piece of rubber hose like 5/16 or 3/8 and put one end in the edge of your ear and run the other end around everything the engine you will hear the leak.

Also the fuel trims on a scantool should have been high since vacuum leak.

 

[getdealtwith]

So that was a pretty big vacuum leak. A good way to hear those is to take a 4 ft piece of rubber hose like 5/16 or 3/8 and put one end in the edge of your ear and run the other end around everything the engine you will hear the leak.

Also the fuel trims on a scantool should have been high since vacuum leak.

Excellent idea. I'll have to try that next time.

 

[getdealtwith]

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.

Did you end up replacing your motor mounts? Did it make any difference?

My mechanic found several other damaged vacuum lines - incl. some that only revealed themselves when he replaced the intake manifold. During that job I also had him install new Motorcraft plugs and coil boots along with injector o-rings. The last bit (PVV elbow), I installed tonight, along with a new PCV valve.

A slight engine shake remains but its rhythmic now. It is present with the AC off or on (off, the engine idles at 780 RPM) but it's noticeable enough for me to want to keep looking even though it may end up being a case similar to Toby's Crown Vic.

One other observation is that there's no difference in the engine shake between P and D or R which I heard may point to a bad motor mount.

 

[RichardH]

Did you end up replacing your motor mounts? Did it make any difference?

My mechanic found several other damaged vacuum lines - incl. some that only revealed themselves when he replaced the intake manifold. During that job I also had him install new Motorcraft plugs and coil boots along with injector o-rings. The last bit (PVV elbow), I installed tonight, along with a new PCV valve.

A slight engine shake remains but its rhythmic now. It is present with the AC off or on (off, the engine idles at 780 RPM) but it's noticeable enough for me to want to keep looking even though it may end up being a case similar to Toby's Crown Vic.

One other observation is that there's no difference in the engine shake between P and D or R which I heard may point to a bad motor mount.

Hmm, interesting on the P, D, R.

I have a very slight engine shake - no codes, good mileage. I know for sure if I put it in N the slight shake goes away. Need to observe in P. Also noticed it's 100% smooth when cold, but at operating temp it's got the slight shakey in D. Very slight and I'm being super nit picky over it. It does go away in N as mentioned.

 

[Aspen03]

I didn't, I ended up having quite a bit to do that day, slid under the truck and did a quick n and out job. I'll try and get back under there tomorrow or the next day. Its very subtle and nothing that is imparing drivability so it hasn't been a big concern. Mileage is good, no issues starting, idling, etc. Obviously it needs dealt with before it does become a larger issue but its been lower on the list than a few other things atm.

I get to play w the vacuum lines on the navigator soon so that'll give me an idea of what to expect on the expy I imagine. I discovered some things re routed in there and may be part of the blame for the ac shifting from panel to dash vents under load. I printed off all the vacuum routing diagrams in all data so I can just start from the top.

 

[Aspen03]

Hmm, interesting on the P, D, R.

I have a very slight engine shake - no codes, good mileage. I know for sure if I put it in N the slight shake goes away. Need to observe in P. Also noticed it's 100% smooth when cold, but at operating temp it's got the slight shakey in D. Very slight and I'm being super nit picky over it. It does go away in N as mentioned.

Mine is essentially this. Very slight. I drive this 50 miles a day, sometimes in total silence just because I want some peace and I notice little things when I come to a stop or happen to be sitting in the lot at work for a couple minutes before leaving. Fwiw I've been in brand new vehicles that have more shake at idle than this.

 

[getdealtwith]

I know this (fortunately) isn't a 3V motor but has anyone experienced a rougher idle before their timing chain tensioners or guides failed?

What about pulley or belt replacements that made a noticeable difference?

I'm also still interested in any cases where new motor mounts actually fixed slight engine shakes when no other symptoms of bad mounts were present.

Appreciate the input!

 

[nema100]

I'm noticing what I would call a very slight shudder at idle - smooth for a few seconds, then a shudder, then smooth, never under acceleration. I thought I felt something before, but the reason I truly noticed was due to the right passenger seat headrest. It would vibrate with the shudder making a noise. Certainly can feel it now that I'm attuned to it.