I have a used 2003 R50 automatic Cooper with less than 55K miles on it. So lately my car has been issues starting up. Like I turn it on and put in to drive and it will struggle to accelerate and move forward. This doesn't happen every time I start but enough for me to start to worry. One reoccurring issues it does have is when I drive slow its twitchy and almost feels like I'm driving stick. Thanks in advance for any suggestions to what might be causing these issues. Any ideas what could be the issue

 

does ECU or EML lamp turned on?

As i guess, the most possible cause are:-
dirty air intake / throttle body
gear box failure
spark plug

 

Check voltage at the battery posts too.

 

CVT transmission. Has the fluid been changed?

 

Yup, sounds like strange CVT behavior to me.