To check for manifold leaks I use a piece of frayed cotton which I pull around all joints if there is a leak it will get sucked towards the leak. Pay attention to the manifold to head fitting area.
as for coils Bosch should be OK though I believe Delphi were OEM fitment
If you haven't already check www.realoem.com put the last 7 digits of your Vin into the search box it will bring up your model. BMW moved from the N43 engine to the N46N I am not sure if it makes a difference to the coil packs or not, worth checking
Thanks again for your advice. I will check all the connectors and loom.
Yes both the coils and plugs were new and all Bosch, thought it best to go for better quality.
Not sure how to check for manifold leaks but will Google.
Thanks again for you prompt advice.
Sadly today that is all Dealers not just BMW "no code no problem"
Years ago had the similar problem with a Volvo T5. I had been in Poland on business, light came on coming back just after crossing into Germany. Volvo dealer could find no fault suggested a faulty O2 sensor, in frustration I changed the fuel filter and ran it with a fuel additive for a couple of tanks. Fault gone and never returned ? I believe it was poor fuel picked up in Poland.
You have also had some pretty extreme temperatures in Spain so could be one of the thermostats having a hissy fit ? Interesting to know if it clears with lower temps perhaps?
The simple fact that you have already had the fault move when swapping replacing parts should tell you something?
Assuming that (a) the coil packs are New and at least OEM quality and correct for the car (b) The spark plugs are new and correct for the car (even a new part can fail) When you were changing those parts you must have disturbed the loom
I would check each connection for continuity while getting an assistant to twist/move the loom
Have you checked the inlet manifold for leaks?
I agree with Dave, get the bmw 1.4.0 … it’s saved me a fortune!
I would bet you have a failed lead or coil. Easy to check.. run the program and it will tell you which cylinder is off. Swap the lead with the next working lead (at both ends) and see if the issue moves, if not, do the same with the coil pack.