My 91 300SE would shake, rattle and roll for a few seconds before stabilizing at idle every time I started the car. New injectors fixed that. Just noticeably smoother idle (I suspect there are other problems). No improvement at speed (nothing to improve).
I replaced the holders as well. It was difficult to fit the o-rings into the groove in the holders but that's as difficult as it got.
An immeasurably small squirt of fuel came out of each fuel line.