Not showing faults is odd if the EML comes on. What software were you using? INPA will show saved codes but some other readers only show active ones. Randomly changing things isn't the best method as you've found.
When I had similar symptoms the fault codes stored pointed to a VANOS solenoid, cleaned it and it helped but then came back. Replaced and all good ever since.
If you're near NW London pop over and I'll scan your car for you. Or you can whip out the solenoids and give them a clean and see if the problem goes away for a bit.
