Hi! Recently my engine blew on my 2005 Mazda 6 2.3. Ended up dropping in a 2009 2.5, everything went well, however, I’m having issues with the idle. At idle it sometimes violently bounces between 400 and 1.2k rpm and sometimes stalls when I slow down to almost a stop and press the clutch down. Still using the 6spd from the 2005 along with the 2.3 intake manifold and 2.3 injectors. Have no clue why the idle is like that, any clues?

EDIT: car runs perfectly above 1.5k rpm