Hi Meabh,
I recently purchased a 2010 Roadster and had the same P0133 error code come up within 100 miles of driving.... first the O2 sensor was changed, but the error still came up after about 20 miles. Currently back at the dealer to see if a solution can be found.......
Will let you know the outcome, soon I hope.
Incidentally I had experienced the inconsistent tick over... spooky
Regards
Mike

Mike
1982 4/4
1999 +4
2004 Roadster S1
2010 Roadster S2
2021 Plus 6