I have an 87 Volvo 240dl with a few very minor mods. The car runs and drives fine but when I go to turn off it doesn’t immediately turn off and often shakes and stutters before turning off as if it was stalling. The mods That I have that could affect this are higher flow injectors an intake and electric fan conversion. I am relatively knew to the Volvo platform so explain things in general terms before going down the rabbit hole of the different Volvo parts between years. Thanks.