UK Car Repair: Astra G 1.7dti 2003 throttle problem, intake hoses, throttle valve

Question
I have a slight problem but it is very annoying. My astra has, let's say, a throttle lag (slow return) on smaller revs. When I release the pedal, rev holds for 1-2 second before dropping or it rises to about 1500 (if it was around 1000) and then drops. It is very annoying when maneuvering and parking because of small revs used. What could be the cause?

Answer
It is likely a throttle valve problem, I would suggest removing the intake hoses and cleaning out the chamber first. It could also be a "lazy" overrun valve on the inlet manifold which is sticking. Other than that the problem is electronic and you would need to get a scan of the vehicle memory to pinpoint it.