I think its the moosing problem.
the st24 also surge on idle called hunting.
A copper pipe end with a 2mm hole drilled in to it.
on the air induction there are two pipes one goes to the intake plenum.
if you put the copper pipe end in there this will cure the moosing.
It's the most common problem to be solved on the mondeo's v6.
A coke 1 lt top would surffice.
simple 2min fix.