Depends on how many miles are on it in that time and whether or not any parts are currently bad. You could also have a, or several vacum leaks.This is going to sound horrible but maybe erm 2 years ago. It was in the shop for a massive stalling problem (left me stuck at a shopping mall for a while...) and had a load of other stuff done to it (new tires, something with the brakes, etc) when it was there, so perhaps it was done then.
If not, then the car hasn't had one in 4 years. I'm horrible I know.