Intermittent rough idle and engine shaking?

[RyanB88]

Hi

2006 N52 on 102k miles

Just replaced the CCV and both vanos solenoids to rule them out

Symptoms - the idle on cold can be rough in that it doesn't sit still and constantly hunts up and down the rev range. Sometimes does this when warm but more so when cold

Every now and then on idle the engine will actually shake side to side for a few seconds, then settle down again

No fault codes at all

No loss of performance that I can detect. Still pulls very well

Any ideas what to try next?

 

[alekos911]

How about a small intake leak, or a faulty coil pack? These two regularly come up as potential causes for rough idle.

 

[RyanB88]

To add to the above problem

Intermittently when warm, but when cold, it has now developed an annoying jerkiness at low revs! I'm sure it'll be connected?

 

[ph001]

I'd defo be looking at coils first too. You would certainly need to rule them out one way or another.

 

[Poltergeist1966]

Had similar problems with a Audi TT - changed all the coil packs and as good as new.

 

[RyanB88]

Hmm might be a good place to turn to. Would they not throw a fault code though if it was the coils?

Today I accelerated in trAffic from first to second gear at around 2000rpm, when changing into 2nd gear the car vibrated and jerked a lot, with it bouncing backwards and forwards. Almost like a dodgy gear change (but not!)

It's quite embarrassing now for any passengers so I hve to get this sorted asap! Thinking plugs and coils next...

 

[z4all]

yeh would expect coils to throw up an error. your scanner is good enough to pick that up right?

 

[RyanB88]

It's Carly, so is considered one of the best

Jerkiness is getting worse and worse, the whole car shakes and stutters on some gear changes now at low revs, then clears and drives as normal...

 

[Flyingfifer]

+1 on the coil packs, possibly sparks as well

 

[Maniac]

Something in the air? (Or fuel) as the saying goes.

My 35i has been rough since the last tank of fuel, only when cold, slight misfires and jerking for around a min or two until it starts to warm up.

Holding fire until a fault develops otherwise I'll waste £99 on a diagnosis that will come back as 'fine when we drove it'

 

[ph001]

Your 35i will almost certainly be the piezo injectors leaking unfortunately. It's quite common not to a get a fault code as well.

OP - just change all the coils. At 100k+ miles they almost become a service item anyway. Worn plugs tends to be misfire under full load acceleration (unless it's a cracked insulator).