Gary, it sounds as if your inter cooler pump may be on it's way out.
But first, the cheap options.
Have you been using fuel with too lower octane ? If so, run a few tanks of premium and see if this clears it. You should be running on premium all the time, these engines can be temperamental if they don't get the right juice !
Secondly, check the fuse for the pump, it's in the box under the bonnet. It's a 5 amp fuse that is known to go now and again.
If it is a blown fuse, replace it and keep an eye on it. The C32 has the same engine and drivetrain as us, but for some reason their fuse is a 7.5 amp one. Don't know why.
If all this doesn't cure it, it's probably your pump that's on it's way out.
Is your inter cooler still original ? If so don't replace it with another oem one, I would recommend getting a Johnsons equivalent, the CM30.
I have one and it's a big improvement !