Have you made any changes that could be related to the problem?
Does your car have a rough/unstable idle ? If not its most likely not a vacuum leak
test the fuel pressure regulator http://www.2carpros.com/dia/test_fuel_pressure.htm
Look very closely at the vacuum tube going to the f.p.r. for cracks and/or leaks
Also check your pcv valve and system, up to 30% of engine intake air can passthrough the pcv system. If its clogged/restricted you will run rich.