thats your idle up vsv,it comes on when you have an electrical load applied ie heaters on,heated rear screen on,brake lights operated and loads more.
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.it allows a small air leak into the throttle body to raise rpm by a few hundred.If you are pinching the pipes and its cutting out then the idle speed screw isnt wound out far enough on top of the throttle body.
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.also if you can hear hissing then the vsv is drawing air from atmosphere.Theres two pipes coming from the vsv,one should go to the left hand side union on top of the throttle body and the other should go to a fitting on the inlet tubing so that its sucking filtered air,it makes no difference which pipe goes where,they are swappable.
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Get the engine to full temp,switch off all electrical loads
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(if necessary remove the electrical plug from the vsv in your picture) and adjust the idle on top of the throttle.
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.now reconnect the vsv and switch your heaters on,the idle should rise slightly.
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All of the above is presuming your ignition timing and idle mixture is set up correctly and there are no other problems,hope some of that helps.
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