I've been getting the P0302 error code every couple of days along with P115C. When it happens the car has much less power, like the turbo isn't working. I assume this is because it's only running on 3 cylinders!
It lasts for a few minutes, then the car recovers and runs OK.
I checked the #2 spark plug, looks fine (they were replaced 6 months ago). It's been raining a lot lately, so I though it might be a moisture issue. I removed the coilpacks and dabbed on a bit of dielectric grease before reattaching (I hadn't done this back when I changed the plugs). Then I went OCD and removed every electrical connector under the hood, dried with a hairdryer and applied dielectric grease before reattaching. The car ran fine for another day, then I got P0302 and p115c again.
Each time it is cylinder #2.
Now the p115c is nothing new - I have had that intermittently for over 2 years and the dealer has not been able to find the problem (I actually gave up and just live with it). There were never any symptoms accompanying p115c. The light would come on and go away after a day.
I don't know whether the 2 codes are related or if its just a coincidence they are appearing together now.
So what should I check next?