What are your settings? Speed, layer etc.

You can cool down a bit to 230. Turn off any part cooling fan if there is one. What brand of ABS?

You are getting irregular cooling of the part. This can be influenced by a bunch of things like infill, supports, wall thickness etc. Protecting the print from drafts , even small ones like air vents, ceiling fans, will help. Having the printer in a room that is relatively warm will help also and a full enclosure is the most hassle free but not mandatory in most cases. Maybe even a heat lamp shining down on the top of the printer but not to close could help keep the air around the printer a little warmer.

ABS is very doable but it does take some work and reading up on.