Misfire on cylinders 123

[Glosboxster]

Please can someone assist me with misfiring Boxster 2.7 year 2000.

Went from running fine to (according to my cheapo analyser) a multiple cylinder misfire detected issue in. Scroll down and it tells me I have a misfire on cylinders 1 2 & 3.

Now all this happened within me slowing for a junction then applying the power.
Juddering, misfiring, spluttering and backfiring.......all in an instant.

So far I have fitted new plugs so that rules them out.....to be honest it is unlikely that all three plugs would fail at once.

Is there a single common component for these cylinders I should be looking at that would cause this issue

Thanking you for any assistance.