Error code, questions, help please?

[Gazaho888]

Hi guys and girls, owner of a 2003 Subaru Impreza, unfortunately a non turbo :( but hey ho, it's a 2.0 gx awd.

Previously had a seat leon cupra 20vt and done a straight swap a few days ago. Now...I got the engine light come on and the error code is P1507, idle control system malfunction (fail-safe) after researching online, there's a few possibilities, some say it's a neutral control switch which comes from the gearbox? And second is a some IACV valve? I don't want to start replacing parts when I don't need to, below I attached 2 images, the first one shows the throttle cable is it? Is it also anything to do with my problem? Is there suppose to be that much slack? And the second image shows a grey plug thats not plugged into anything, can someone tell me where this is supposed to be connected to? Maybe this is my problem of the error code? 

It's not causing me any problems just eml light keeps coming on and I'll just keep turning it off...no idle problems I don't think.

Thanks in advance guys!