1998 Audi A8 4.2 Running problem
 

I have a 1998 Audi A8 that shuts off intermittently. The car will start up every time and if I leave it idle it will shut off after a varied amount of time. When driving the car as long as my foot is on the gas it won't shut off. It usually will shut off when I take an off ramp off the highway and am coasting. I just don't know because it's so sporadic. I replaced the fuel filter and put a new battery in it. The breather hoses were replaced also. Any help is much appreciated.