my '03 element is experiencing a surging idle. when i turn the engine over the engine idles high, at above 2k rpms. tapping the accelerator will bring the idle down to normal, but then it will rhythmically rev from less than 1k to above 2k rpms at about 1/sec. furthermore, even at highway speeds this variable, rhythmic idle persists when i'm not jamming the accelerator. any ideas about what might be causing this issue???