Car sporadically drops in rpm when air conditioning is on.
 

I have a Hyundai accent active 2017 which has done only about 40,000 km. It’s been a great car so far! In the last few months I’ve noticed when I have my car in park, whilst the air con is on either the 1st or 2nd setting it’ll spontaneously drop quite significantly in revvs where it feels like my car shakes for a moment, then bounces itself back up. It doesn’t always happen either, but I have noticed it more as I do wait for my daughter in the car or when we randomly have to wait. It feels like the car drops so low in rpm that my car could stall, but it doesn’t. The air con works fine otherwise, whilst driving there is no issue. I took it to a mechanic and he said he honestly doesn’t know, but to maybe try a different petrol station as it could be contributed to water in the fuel? Which, I don’t think but I don’t know what else to do! It’s so strange but he saw it happen and said it’s definitely not normal. Any idea? Has anyone else experienced this? Thanks

The issue might be with the idle control system, especially since it happens with the AC on. It's less likely about the fuel quality. Consider checking or cleaning the idle air control valve, and look for any software updates from a Hyundai dealer. A clean throttle body and checking for vacuum leaks might also help.