1998 Boxster P0301-P0303 odb 2 reading

[vangelo74]

I just got a check engine light come on last week, plugged my obd 2 reader and it says P0300-P0303 cylinder misfire.
The car starts up perfect rev as usual on idle no hic ups or anything, but once i drive it and push the thottle it starts to stutter and smoke out the back. I called my garage and explained the whole thing, he says the timing jumped on 1 bank cylinders 1-3. Probably due to a worn out chain guide.
So my question is has this ever happened to anyone here or can it be something simply. My plugs and coils are new less the 2000 km, and i checked the oxygen sensors. So i have an appointment next monday at the garage but just wondering if anyone can help.

Thanks