I am having idle surging problems with my Nissan 2004 Altina between 1500 rpms t on 2004 Nissan Altima

Idle surges between 1500 rpms to 2000 rpms. have done the Idle Air Volumn control relearn, still idles same. There is a Vaccum switch on top of engine just behind Throttle Body with 2 Vaccum lines coming out of it. What is this switch called? and could this be a problem with the idle? I have pic's to send if responded to

Asked by for the 2004 Nissan Altima
scan codes and post so we can adv
Scan Code is P0507
4/27/2013 UPDATE!!! I changed the Throttle Body and performed the Idel Air Volumn Relearn and all is better now. Idle is at approx 450 rpm's way too low now but no more surgeing. Also was VERY hard to start, Changed spark plugs, starts somewht better but still takes longer than normal to start, looks like the fireing on plugs is weak. Any suggestions on this. Got NO Check Engine Light now.
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