Misfires

[Nyyyko]

2012/13 155 tsi, 145kkms. Starts fine, after about 4 sec I get intermittent misfiring in two of the cylinders. Replaced Plugs and coils. No issues while driving, only at idle. Pcv? There’s a fair bit of vacuum if I remove the oil cap, no whistling though. Good L/100. Small leak in rear main seal? Just noticed a small oil leak under the engine side. Thoughts?

[bwilkeson]

Recently replaced plugs and coils to NGK BKR7EIX and VW R8 redtop coilpacks. .27 plug gap, has developed a slight miss at idle but not under load. Only 33000 kms. Unsure where to look for answers with our issue here.....

[Nyyyko]

Recently replaced plugs and coils to NGK BKR7EIX and VW R8 redtop coilpacks. .27 plug gap, has developed a slight miss at idle but not under load. Only 33000 kms. Unsure where to look for answers with our issue here.....

I am wondering if there is an issue with the intake manifold flaps, apparently there’s an updated version in 2017, oooor carbon buildup oooor injectors. As it is only 2 of the 4 cylinders this would indicate a point specific issue rather than a global.

[tigger73]

Misfires could be a number of things.

If your spark plugs aren't gapped properly and/or bad plugs will cause it.

Also for higher mileage (>100,000km) then carbon buildup can cause this sort of thing too. Either way walnut blasting is a good preventative measure and will make your car run better and improve the fuel economy so it'll pay for itself in the longer run (well helps to justify the expense).

[Nyyyko]

Misfires could be a number of things.

If your spark plugs aren't gapped properly and/or bad plugs will cause it.

Also for higher mileage (>100,000km) then carbon buildup can cause this sort of thing too. Either way walnut blasting is a good preventative measure and will make your car run better and improve the fuel economy so it'll pay for itself in the longer run (well helps to justify the expense).

ima pull it apart soon and decarb... soak and scrape

[simon k]

I'd swap back to the old plugs and coils before I did anything else. That's the cheapest and quickest way to diagnose

[Nyyyko]

The Idle misfires in 2 and 3 dramatically improve when ac is switched on. To me this indicates carbon more so than anything electrical, mechanical, vacuum or a seal. Thoughts? There is no issue when driving. Engine is strong, smooth and responsive.

[tigger73]

Yeah I'd be getting a carbon clean anyway at 145k regardless then see how you go from there. It's something that more than likely needs to be done. If it hasn't ever been done before then it's definitely overdue.

[Nyyyko]

The quest continues. So far I have replaced the spark plugs, ignition coils, I mechanically decarbed the intake valves and manifold. Today I replaced the PCV valve which has reduced the vacuum in the engine but the misfires continue. Turning on the a/c improves but does not eliminate the random misfiring. I’m
thinking vacuum leak/air leak somewhere? Timing chain guides wear? Thoughts? Oh, and the small
Oil leak was a reused oils drain Comp washer... replaced and good to go.

[Nyyyko]

To add, I have a high fuel rail pressure code. Maybe this all leads to my injectors going bad? I cleaned them when I decarbed and put a new seal kit on them. I’m wondering if maybe the ecu needs to adjust after changing the PCV. Vacuum is way down to where is should be. I’ll drive for a while and see if it improves.