You might get troubles with the engine "hunting" upon idle/tickover. It might even stall every once in a while. I'd get it fixed. I am not sure but maybe the ISCV on the 2.0i DOHC (8v) Sierra is the same? Plenty of those available I'd say.

I was just thinkling, AFAIK the ISCV hardly ever really breaks. Is the hose connected properly? Maybe it's split? Or the gasket on the ISCV wasn't sealing properly?