1997 Jaguar XJ6 stall problem

The car idles fine. When you try to take off the car buckles then when you take your foot off it goes back to normal idle. It does this real bad when it's cold but when it warms up it does it less and sometimes it does not do it at all once it's been running for a while. And to add if you unplug the mass air flow sensor the car takes off fine!