misfire - any ideas ?

[batty]

hi guys

the S4 has picked up a misfire - it seems to be missing a beat on the n/s cyclinder bank at very light loads just off tickover. you can hear it popping and farting somewhere on that side.
everything seems fine under power.
also worse when cold. i took it to the local specialist & he says there's no fault code logged (i don't have vagcom)
he's going to try it again when cold

it doesn't seem anywhere near bad enough to be a coilpack - i had one go on my S3 and the engine ran like an absolute bag of nails..!!

any of you guys got any ideas ??

[spurtle]

I've had that - took a while to sort out but replacing the plugs, PCV valve (which was completely blocked) and front lambda sensors fixed it. It was really difficult to diagnose because it wasn't logging misfires or faults - but it definitely felt like a misfire.

Also might be worth changing the fuel filter if it's never been done.

[dazzer]

Did you get this sorted Steve?

[batty]

hi dazzer

2 garages failed to solve

I've got a new coil pack on order, so will try by process of elimination.

[dazzer]

hi dazzer

2 garages failed to solve

I've got a new coil pack on order, so will try by process of elimination.

Expensive trial and error mate! Give me a shout if you need to run VAG COM over it and some real time logs. Can also try some bits off mine within reason.

Which garages did you try out of interest?

[batty]

thanks for the offer, mate
i won't name the garages, as it wasn't really their fault.
the first put their scanner tool on it and couldn't see a fault, but did notice a throttle hesitation when driving. they offered to try several sensors one-at-a-time but rightly warned me it could be expensive as the sensors can't be returned if found not to cure the fault.
the misfire is only at cold, although both garages kept the car overnight.
i think they didn't really see the slight misfire at cold as a problem - but you know when your own car's not right..!!
but the "hesitation" issues has put the seed of thought in my mind and it won't go away....the car has never had "sharp" feel on the throttle - goes perfectly at wide-open-throttle - but response is a bit woolly.
hmmm....

[dazzer]

thanks for the offer, mate
i won't name the garages, as it wasn't really their fault.
the first put their scanner tool on it and couldn't see a fault, but did notice a throttle hesitation when driving. they offered to try several sensors one-at-a-time but rightly warned me it could be expensive as the sensors can't be returned if found not to cure the fault.
the misfire is only at cold, although both garages kept the car overnight.
i think they didn't really see the slight misfire at cold as a problem - but you know when your own car's not right..!!
but the "hesitation" issues has put the seed of thought in my mind and it won't go away....the car has never had "sharp" feel on the throttle - goes perfectly at wide-open-throttle - but response is a bit woolly.
hmmm....

Fair enough about the garages. Let me know if you want some VAG COM help.

[jimbo1234567]

it could be the coolant temp sensor thats goosed . if so it will tell your ecu that the engine is warm when its cold and not give enough fuel(choke) hence the misfire/hesitation when cold. thats a simple /cheap fix