Misfire on Idle

[Dan_6921]

How's it going everyone, I'm new to this forum. I'm having a misfire on idle issue with a GTI (BWA engine code). The misfire is noticeable when the car is up to temperature and it only happens on idle. The issue has been there since I got the car. I had the engine forged as I'm planning on going high power but I still have the misfire issue. The belt and chain was done when the engine was sent off for forging, I put in a brand new set of iridium spark plugs and also new R8 coil packs. I've replaced the cam follower, injectors, new PCV and charcoal canister. I've checked for any possible boost and vaccum leaks and everything seems to be fine. Also had upgraded the diverter valve, yet I still can't find the issue. Anyone have any ideas or may have encountered the same problem before? Thanks looking forward to your replies.

[Clarkj93]

Really common result of injectors. But you've changed and checked everything else I could possibly think of.... so if it was me and its only minor just stop idling and drive fast:grin: Lambda sensor maybe would be my absolute last guess.

[DBXdarkangel]

Was they new bosch Injectors or used ones or cheap ebay ones?

[mjmallia]

Mine was initially caused by carbon build up on the intake.  The second time I had idle issues related to the oil rings that regulate the cam adjuster.....the inner one was broken for me.  They were damaged after the chain and adjuster was done, but it did not immediately show up as an issue.

[pudding]

Yeah it's super common for those stupid rings to break. Heat cycling and oil soaking makes them ultra brittle, but to be fair, they're only meant to be fitted once anyway.  They should always be replaced if the chain cover comes off 

On mine the middle one broke, which caused a god awful rattling just off idle when hot.  The VVT still retarded and advanced according to spec though. If the inner or outer ring breaks, that's when you can get "Slow response" or "Set point not reached" type fault codes.

OP - check the plugs for colour and wetness, which would indicate fuelling or oil getting into the combustion chamber issues.  They should all be dry and the same colour.  As you've attacked the usual suspects already, there's not a lot else to check and I'm just hoping it's not a mechanical issue. Damaged valves and/or a broken piston ring or ring land can cause persistent misfiring.

[Dan_6921]

Was they new bosch Injectors or used ones or cheap ebay ones?

They were brand new bosch injectors

[Dan_6921]

Really common result of injectors. But you've changed and checked everything else I could possibly think of.... so if it was me and its only minor just stop idling and drive fast:grin: Lambda sensor maybe would be my absolute last guess.

That was replaced also I forgot to mention, I had the same suspicion that it could have been faulty.

[Dan_6921]

Yeah it's super common for those stupid rings to break. Heat cycling and oil soaking makes them ultra brittle, but to be fair, they're only meant to be fitted once anyway.  They should always be replaced if the chain cover comes off 

On mine the middle one broke, which caused a god awful rattling just off idle when hot.  The VVT still retarded and advanced according to spec though. If the inner or outer ring breaks, that's when you can get "Slow response" or "Set point not reached" type fault codes.

OP - check the plugs for colour and wetness, which would indicate fuelling or oil getting into the combustion chamber issues.  They should all be dry and the same colour.  As you've attacked the usual suspects already, there's not a lot else to check and I'm just hoping it's not a mechanical issue. Damaged valves and/or a broken piston ring or ring land can cause persistent misfiring.

I see where you're coming from, everything at the moment is basically fresh on the car as I only drove a few thousand km on the built engine so it's weird that the problem persists. I just hope it's nothing to do with the ECU. Thanks for your response

[Dan_6921]

Mine was initially caused by carbon build up on the intake.  The second time I had idle issues related to the oil rings that regulate the cam adjuster.....the inner one was broken for me.  They were damaged after the chain and adjuster was done, but it did not immediately show up as an issue.

I had the carbon cleaned and those oil rings replaced also, I just hope they were not damaged when new ones were put on. I did test the cam position in relation to the crank on VCDS and it was only -1 degrees off so it's fairly spot on.

[mjmallia]

Mine were replaced also when the chain and tensioner was done, but one must have got damaged on fitting......very easy for them to stretch on fitting, and when sliding it back on they can catch or in my case a ring snap but stay in place without realising until it eventually dislodged itself and caused issues.  Thankfully found the missing part