Strange misfire at idle.

[welshname]

Since I got the car there has been an odd misfire at idle. This can be seen on the revs and you can hear it in the engine bay and visibly see the engine shake as it does it.

It isn't to any sort of pattern, I.e it doesn't do it once every second or whatever, it'll do it once, then wait a second then 3 or 4 times consecutively.

So far I've replaced:
Plugs
Coil pack
Leads
Lambda sensor (pre cat)

I'd get a video but you've no chance of hearing it over the dephaser.

Last thing is that you don't ever notice it at any other time, car made good power on the rolling road and has no related faults in the ECU

 

[Tommo.]

Could be an injector on its way out?

 

[welshname]

That's the only thing I can think. Ive got an RS tuner so could look at the live data but wouldn't really know where to start. You can see on idle the ignition timing retarding as it bogs and the lambda reading drop into what it flags as a red colour which is what made me think lambda.

When I went to EFI to have it RR'd he said on the first 2 runs the car hesitated to come on open loop when it usually would at 4k or whatever it should be, which again made me think the lambda is off.

 

[burtt]

Have exact same problem, I was thinking injectors. I'm considering an RS tuner just to check it out and map it while I'm at it.

 

[fishmitten]

I have the same problem too , I just thought it was how they tick over , although I do have a ticking noise that is coming from somewhere that's driving me crazy .

 

[barnesautos]

If you suspect it's an injector - it's quite easy to diagnose.
When you pull off the electrical plug for the injector that's suspect -the misfire on 3 cylinders will be a constant NON upset mis.
If you pull off a working injector the mis will be the upset mis.

Hope this helps