DIYPNP '96 1.8 - Intermittently running lean
 

Apologies if the wrong section, this is likely a more general issue than MS, but thought i'd start with the Log and see where it takes me!

So, over the past few weeks I have started having an intermittent running issue, with increasing frequency. On my ~30min commute it'll go super lean (AFR ~18-19) and run like a bag of spanners for a bit. If I can, I stop as soon as I can, but often I can't on my commute (sat in traffic in London).

I started this log when it was happening, at approx 30 seconds in I was sat at traffic lights at idle so it's a little clearer: https://www.dropbox.com/s/ocbr0zfjb7...Issue.msl?dl=0

Any thoughts on a logical place to start? Fuel Pump, or misfire caused by dodgy coil pack?

Thanks for any input in advance!

Car Spec: '95 1.8, DIYPNP MTX-L, MS2, T28, Injectors, EBC etc etc

I turboed the car Mid-2014 (RR tuned at the time) and it's been running great ever since, have not had to give it much attention aside from usual servicing. Recently fitted a Metallic Sports Cat and it now sails though the UK MOT Emissions checks with no issues. Cleaned Air filter, and fitted new HT Leads and Fuel Filter recently for MOT.

Do you have a data log of it idling at the correct AFR to compare it to, along with a copy of your tune?

I would suspect a heat soaking air temp sensor if this typically happens from sitting in traffic. But Matt is right, we definitely need a "good" log to compare.

Fair point guys, I'll do another log on the way home tonight.

I've not had this problem before and have had the car on the road for over 2 years! For info, my IAT is mounted directly in the end tank on my FMIC.

When I left work this evening it was running rough as soon as I started it. Paused by the side of the road and gave all the leads around the ingition/injections a good prod and it seemed to clear up idle normally. Took a brief log sat idling before I took off:
https://www.dropbox.com/s/0dd9yytsgq...lIdle.msl?dl=0

Once I got home I did the same (So a bit warmer): https://www.dropbox.com/sh/xi49696eq...TUC9kuIoa?dl=0

It feels like a misfire, so will try a second Coil Pack I have sat in the garage. It didn't feel like it changed much when I disconnected Cyl 1 injector (but by this point I'm not sure if I was imagining it), so i'll take a look at the Connector. As a side, new Spark Plugs are in the post so i'll gap and slap new ones in while i'm at it.

Oh yes, my Current Tune: https://www.dropbox.com/s/dcez4931e4...01.42.msq?dl=0 (Critism welcome!)

A misfire can definitely cause a false lean reading and if the coil has a problem, it will be more likely when warmed up - definitely try the coil at this point.

So...after all that it seems the Coilpack has sorted it. Have done 40 odd miles on the replacement pack with no issues.

Thanks for responses, I probably went over board with the logging, I had a little panic seeing it go lean on the WB.