V6 vibrates slightly while idling

[MarkoM]

Hi all!
I recently bought a 166 2.5 V6 and I have noticed that the engine vibrates very slightly but regularly every 15 seconds or so when idling and that the rev counter oscillates every time this happens. Any ideas what the problem might be? It is hardly noticeable but shouldn’t the engine be vibration free?
Thanks,
Marko

[James76]

Sorry to suggest what sounds like a daft idea but....

Is it the air con compressor or aux fan cutting in, and the engine receiving extra load? Can you hear a definite relay click just before? Mine doesn't do this noticeably but the V6 does idle lower that the JTS. They all have wee habits, the JTS hunts on a warm restart for about 10 seconds.

Just a wee idea to dispel before you go thinking there is something really wrong.

Just thinking - even a Nissan X trail Diesel does exactly this with the air con on - it floats about by 200 rpm at idle with this happening.

[Mitch916]

The only thing I have had that gave vibration while idling was the dog bone engine mount (top, left of engine bay) worn. That wouldn't affect the revs though........

[purple145]

I too thought my V6 would have been silky smooth, but its not, so I just let it fizz and rasp instead

[Dougie166]

Uneven tickover - Hunting, Could be an idle control issue? As mitch says it is worth checking the dog bone (or other engine mounts) - even if hunting the vibration should not be transferring through car.

PS - The dog bone sits above the cam cover to the rear and attaches near suspension turret, easy 5 minute change (£30 part from Alfa), mine was shot and changed a couple of weeks ago, much smoother now!

[Alfapug]

I'm no expert but I too would also suggest looking at the dogbone mount (top left of engine). Mine wore out on my 156 2.5, my mechanic told me it was quite common to need to replace it - as Dougie says, its not too expensive and it'll probably need replacing at some time in the future anyway.

[Icheb]

Agreed, changed mine 5 months ago, £25 inc. VAT and a 15 min job with a spanner.

[MarkoM]

Thanks guys!
It is not the aircon, that was the first thing I checked. Funny thing is that it only vibrates at normal idle rpm (ca. 625 rpm); there is no vibration at say 800 rpm. Anyway the car is going to be checked by a local AR specialist on Friday, I will report the findings.
Regards,
Marko

[symon]

My TS does it slightly, the revs go up and down by about 50rpm evey 15 seconds or so.
I don't think its too much to worry about, if it was a lambda or maf sensor it would probably have failed the emissions check, which it passed with flying colours.

It could be a sticky idle control valve, but this often causes the car to stop all together.

It may also be worth checking for air leaks, after the MAF.

Simon.

[Dougie166]

Originally Posted by MarkoM

Funny thing is that it only vibrates at normal idle rpm (ca. 625 rpm); there is no vibration at say 800 rpm.

Sounds like the answer to me there - The idle should be around 800 to 900rpm not 625. The car is just about to cut out hence the vibration - Simply needs idle increased.

[CrispDust]

Stated idle for V6 is 750rpm.

[Dougie166]

Checked mine today - Runs smoothly at just over the 750 mark, I would say an indicated 800 to 850.

[MarkoM]

It was MAF! Just been replaced with a new one and now it runs as it should.
Thanks for the suggestions!
Regards,
Marko

Was just going to say that. Mine is doing exactly the same and I've been told to get the MAF changed. How much did it cost by the way?