Stagea S2 RS Four S Misfire/Rough Idle

[deev236]

Hi All,

First post here, hoping someone can help me with an issue that seems to come up a lot with RB25 NEO Skylines & Stageas but without any clear solutions (I've read through about 20 threads at this point on SAU).

So, seemingly a common issue - my Stagea is misfiring while at idle, with a pretty frequent backfire as well but no other noticeable misfires or problems when driving around/under load. 

The misfire has presented basically as a small dip in RPM's every few seconds while idling, minor but consistent. It's significant enough to feel the car vibrate every time it momentarily drops down by around 50-80RPM before it pops back up again to around 800RPM.

I've replaced the Ignition coils with Splitfires, new spark plugs gapped to 0.8mm, new O2 sensor and new MAF sensor after ECU diagnostic has shown error codes relating to Primary ignition, O2 sensor and MAF.

Something that I found strange was that when the MAF/AFM is unplugged, the idle does seem to smooth out. This is why I replaced the MAF/AFM but it seems like it's not the cause of the issue.

Next step I guess would be a flow test and possible replacement of injectors, but I'm wondering if anyone else has had this experience and if they solved it, what the solution was for them. 

Appreciate everyone reading through, I have done very extensive research online to try and fix this issue but haven't really gotten anywhere.

Cheers!

[GTSBoy]

The loom and its plugs.

[deev236]

Do you mean the Ignition Coil Pack Loom?

[GTSBoy]

Yeah, and the AFM, and the injectors.

[deev236]

Cheers man, just ordered the ignition coil loom will see how that goes. the AFM loom connector looks pretty old and crusty so might have a go at repinning a new connector and checking the wires. just gotta work through everything until I find the issue I guess!

[deev236]

Okay so I replaced the ignition coil loom with no luck. Took the car for a test drive around the block and it sputtered a bit in the lower revs and continued to idle rough when I stopped. 
 

Any other ideas? I'm guessing I'll have to look at the injectors next.

[Stick180]

Checked for vacuum leaks?

 

[pber13]

Deeve, I don't suppose that you've made any progress on this? My Stagea has the exact same problem, and just like you, I've read through as much as I can online, with no real progress. My car isn't throwing any codes at all, which is a little frustrating. I've changed plugs, checked the wiring and harness. A new MAF gets here next week, but I'm not hopeful it will solve the issue.

[deev236]

Hey pber13, unfortunately still no luck. At this point the following has been done with little or no success:

- Spark plugs replaced, gapped to 0.8mm

- Splitfire coilpacks installed to replace originals

- Replaced Ignition Coil/Coilpack harness with a new genuine nissan one

- New fuel filter

- Replaced AFM/MAF sensor

- Injectors have been thoroughly cleaned with an online flush (without removing)

- Upper engine and inlet decarbed - blew tons of black smoke out, cleared the carbon deposits from the top of the engine and exhaust. 

- IACV removed and thoroughly cleaned with carburettor cleaner

- O2 sensor replaced with new and genuine one

-  Smoke test revealed no vacuum leaks

- Healthy compression test of 160psi across all 6 cylinders

Overall the car does run a lot smoother now, no backfires between gear shifts like it did originally... but the rough idle when warmed up is still there. It may not even be a misfire but simply a rough idle.

Seems crazy to me that so many people have had this issue and seemingly no one has gotten to the bottom of it, or at least never bothered to post if they did!

Hope you have more luck than I did pber13, I'm at a point now where I'm just going to try to ignore it unless it gets worse. Would love to fix it but I've genuinely run out of ideas of what it could be.

[deev236]

And by the way, I've also checked the ECU diagnostic numerous times and got a bad O2 sensor code and initially an Ignition Primary code, which is why I replaced the O2 sensor and all the ignition components (coil packa, plug and loom). No codes have been coming up lately despite the ongoing issue.