I've been studying for my aircraft tech ground exam and reading about the hazards of over-leaning the mixture. It brings to mind a time when I did a solo flight and managed to taxi to the holding point and do power checks with lean mixture, right up to the point where the checklist told me to check 'Mixture Rich'. I had noticed it seemed to be rough running, and of course increasing to full rich sorted that out. Now I've read about the theory, I'm wondering if I did damage to the engine. How would one know?
As has been said running the engine lean at idle/low RPM while taxying will do the engine more good than harm. But before power checks or advancing the throttle you must put the mixture back to fully rich, otherwise the engine will start to pink, as you found... you probably didn't damage the engine, I think repeated abuse would cause a failure, but you won't be able to tell until the donk one day suddenly goes bang.
That said there are signs of repeated running on too-lean a mixture, valve seats getting burned etc.
Amazed how few people are taught how to use the big scary red lever.
Smithy