It's a typical SCV problem. On a couple of occasions, leaving the fuel cap loose (not tightened all the way down, maybe left about halfway in) has relieved it. Another symptom is that the idle is not smooth, but you can hear the engine doing little surges.
If that sounds like your problem, fuel injector cleaning products may help and they're a cheap fix - they'll also never hurt! There are two that I trust to use, both by Liqui Moly. The first is a "add to the tank" product, "Fuel System Treatment" which works for petrol and diesels. When my engine started that idle-hunting, I used a bottle of this in my tank (admittedly I only had about 30 litres left in there) and drove it - after about 100km there was a distinct improvement, and the problem was gone after 200km.
The other product is their "Diesel Purge". This is a little more complicated because you have to disconnect fuel hoses from the filter and run this directly through the system, but it's really very intensive and does an excellent job. It's been used by quite a few members of this forum in the past and there are videos of the procedure - like
this one.
Neither product will cause any damage to the engine, and while they might not fixx a damaged SCV, they'll clean a dirty one and clean your injectors as well, so no harm done and might fix the problem.
Of course, it might not be a dirty SCV, which could be damaged and need replacing anyway, or the problem is in some other part of the system - like a possible fuel starvation issue, or a failing turbocharger. Have you noticed any smoke while this is happening, and what colour is it, if any?
