My 2005 1.6 vct engine focus is a little poorly, Symptoms are random lumpy idle, and pre ignition/rattling when put under load in a high gear. No EML, but a scan shows pending codes P0172 and P0175. Short term fuel trims are  pretty normal and long term are around -10%, O2 sensors also look to be functioning normally. I have checked the vacpipe that runs from the inlet manifold to the PCV, and the valve itself. Is that the only vac connection?

Any help would be appreciated.

many modern cars have knock sensors, they wind back the spark to reduce uncontrolled burning.  no idea if a basic old car like the 1.6 has it

what quality is the fuel? condition of the plugs and the compression of the engine?

I have a 2.0 tdci 2013 and it also pinks. Not all the time. Only in 6th gear usually on motorway under a bit of pressure. Don't know y.  It pisses me off. I usually take my foot off the accelerator a bit

as an experiment I would try the more expensive premium fuel to see if that stops it.  I have not had a car pinking for years.  one of the factors in the past that could cause it was a build up of carbon in the combustion chamber that would glow red hot and ignite the compressed fuel/air mixture before the spark plug sparked.  you don't hear of the need for a decoke these days. 

I'm confused because the codes indicate rich condition, but 'pinking' is usually associated with 'lean'?

9 hours ago, isetta said:

as an experiment I would try the more expensive premium fuel to see if that stops it.  I have not had a car pinking for years.  one of the factors in the past that could cause it was a build up of carbon in the combustion chamber that would glow red hot and ignite the compressed fuel/air mixture before the spark plug sparked.  you don't hear of the need for a decoke these days. 

thats very true, I suspect that has a lot to go with use of unleaded fuel though. I have driven many petrol focus, and many of them could be made to pink. I wonder if it's a byproduct of cars designed to run as lean as possible for economy reasons