Troubleshooting engine vibration at idle

[designforlife]

Mitsubishi 4g92 engine, fully serviced recently, it's exhibiting a fair amount of vibration at idle, only when warmed up(seems smooth when first started up, then vibration creeps in).

Enough vibration to feel it in the seat at idle, and you can see it in the block with the hood up...during normal driving and revving, it goes away.

The idle isn't hunting around, and is a steady 800rpm as it should be, although you can feel a little rumble/rise in vibration every now and then which makes me think is it a very slight misfire?

Car is running and performing well otherwise, pulls as it should. No CEL or error codes coming up.

I've sourced a new PCV valve which should be coming in a week or two, as the car has done 135k and I doubt the original one has ever been changed...anything else I should be looking at?

ta.

[PositronicRay]

Plugs?

[designforlife]

Had some fresh ones when serviced (circa 2 months back), and they're definitely the correct spec...NGK iridium yadda yadda, took me a while to source them (stupid unusual car).

[designforlife]

It also had fresh leads at the service(magnecors)...i could always swap the old ones back in to rule those out i guess.

[anonymous-user]

Have you checked all thee engine mounts? Failed mounts result in much more transmitted vibration, especially at idle.

[designforlife]

The engine mounts did occur...but it doesn't vibrate from cold, only once the block is warmed up after a few minutes...if it was the mounts it would vibrate regardless of engine temp?

I will check them anyway as they probably could do with changing on the car (20 years old).

[Allan L]

Is that one of the Mitsubishi motors with the Lanchester harmonic balancing system (trendily called "Silent Shaft")? If so perhaps the balance shafts have been wrongly assembled, or their drive has broken.

[designforlife]

a quick googles suggests not, which is just as well cos that sounds like a nightmare to get sorted.

[toohuge]

I'm not 100% on Mitsubishi engines - but do you have any dual mass rotating components on this engine ? Either flywheel or crank pulley? If it's on its way out- it'll begin to vibrate when warm. We had a similar set of symptoms on a ford recently. Nightmare to find as it was in the crank pulley.

[designforlife]

Not that anyone probably cares, but finally resolved this today.

Vibration was a slight misfire, caused by valve clearances set too tight. Had them adjusted properly and it's cured.

[E-bmw]

We may not seem particularly interested now, but at least you have told us all what the problem was if anyone searches for the same issue in the future, thanks for that, not all do.