ABS residue can be an issue when switching to pla. The thing to remember is the difference in temperature for your hotend between the two. So when you switch to pla have the temp at abs temperatures and then manually extrude a length at that temp before starting to print at pla temps. sometimes it works sometime it doesn't.
Rebekah thats a really innovative idea I think i might have to start doing that... I wanted to get a set of new nozzels anyway, so I could play with difrent nozzels for fun and quality/speed... but now I see a practical aspect too thanks for that