E87 N52 130i - Misfire Cyl 4 Problem

[jinsta]

Long story short, had misfire on cyl 2...swapped coil to 5 and fault followed so replaced single coil with Bosch one (matched other 5 as were bosch) and as i had it all open, also fitted 6 new ngk spark plugs. Cleared codes, ran all good and thought that was that.

About week later, got EML/misfire issue pop up again…but now on its on cyl4

When initially start up its running fine, no eml light, but after few secs get bit of light shaking and if i rev pass 3k, eml comes on. Get the following codes:

2E1B - Firing, Cyclinder 4
29DO - Cobustion Misfires, Cyclinder 4

As the original date fitted for 5 of 6 bosch coils is a bit unknown (before my ownership)...thought sod it and just bought/replaced all the coils for 6 new Delphi ones (now the oem for pn)…but still getting misfire/fault on cyl 4.

Hmm, so then swapped coil (and sparkplug) around with cyl 1 as thats got no issues and still get same fault code, again only related to cyl 4.

At this point, I can rule out coil and spark plug being at fault. Also seems to run exactly the same with cyl 4 coil just unplugged so next thought was perhaps it could be wiring to the coil for cyl 4.

I gently used little flat head screwdriver on the wiring connector plug (loom side) that goes to the coil. In my mind, i’m trying to make the connecting pin tighter, but its so small not sure what the screwdriver was actually doing other then lightly scuffing up the connecting pin...but...whatever it did when refitted plug/started back up…cyl 4 is no longer misfiring.

I cleared codes, went on a good spirited drive and perfect, was running fine again. At this point, all seemed good so refitted everything thinking it was sorted.

So that was all yesterday and this morning went to start up from cold and after few seconds...experience exact same misfire issue again and codes relating to cyl 4. I let it run for like 5 mins to just warm up the car, cleared codes and just like that...no more codes and running mint again.

Dubious this was sorted, i've let car sit all day and its now evening...gone to start it again from cold and...EML lights back on again after few seconds and same codes are back. If i let warm up...clear codes, its fine again.

I can rule out spark plug/coil and although not formally tested, also both having low compression/faulty injector...as no way if these were shot would the car run fine when codes were gone.

I suspect its the loom, but strange it works fine once warm. Could poss have some sort of break in connection somewhere i guess that somehow self rectifies when warmed up...dunno though.

Anyone here ever had issues with N52 coil loom? or even have a PN for one. Failing the loom at fault...what else could this be.