2.8 and under acceleration only...hard to tell but it seems to be from the passenger side more than drivers...will go away and no signs of it even going up hills...then come back..very random..car runs fine although a little rich
I think your comment about running rich is the key. If you get a lot of carbon deposits in the cylinders....valves...etc. you will get detonation under some circumstances. If there is no SES light, it's not bad, but over time it gets bad. Could be the CTS is a little off, so the computer is making things too rich. Could be that your timing is a little off so things are not burning up completely. A cheap attempt at a fix might be some injector cleaner in the fuel.