No, absolutely not a for sure thing. Could be several other things, which someone more familiar with your car would need to help you with, such as an injection system problem.
But vacuum leaks are a rather common ailment. So it's one of the first things I check for. They can kind of happen overnight, but usually will come on slow as a hose or fitting drys out and cracks. But it may not make a noticable difference until it reaches a certain point. Who knows, maybe you hit a bump in the road hard enough to jar something. Or you checked the oil and nudged a hose just right. Ect, ect.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)