Previously it was due to cheapo lambda's fitted, a change to new genuine ones sorted that. On my way back from Devon recently it started pinking a little on part light throttle. Before going down the compression / leak down test for HG issues I thought I'd take a look at changing the coils and plugs. In short there was a mixture of old bremi and 1 new bosch coils so I changed them all for new bosch ones (£17ea ebay). The plugs were well worn ngk dual electrode ones so I changed them for a full set of ngk iridium ones (£38 per set ebay).
The car now starts and idles so much smoother, unbelievably more I'd say. It's super smooth on the road too. It's not been this smooth to drive since I bought it. NO pinking either
Just a pointer if anyone else is or does in the future experience slight pinking, MAYBE try this first
