could be if someone had it wired up funny. but not likely, because if it was on all the time, it would always be running at 1500 rpm and would contine to run at 1500 even after you rev'ed it up. it's normally set at 1050rpm i believe. what it sounds like to me is that you running on your fast idle cam and after you rev the engines it's trying to run on the idle setting that's set too low. or you have an egr valve that stuck open. here's a basic vacuum line drawing.
