V70 P2 engine system service required

Hi chaps, why is my 'engine system service required' message coming up with
an orange warning exclamation mark every third engine start?
There are no OBDII codes and the engine works fine. I've checked things
like the oil level, listend for air leaks in the intake system. I've taken
off the throttle body for a good clean, which did improve the response
quite a bit, it was quite gunked up with tarry oil deposits. Had to do the
throttle relearn thing(switch on ignition, engine not running, press slowly
on throttle to full throttle and repeat) because it was idling high after
the clean. Now idling perfectly. Not even a drop with the air con switching
in and out. Changed the air filter too.