I have a B20b swap in an eg hatch and I’m having an idle problem. When I’m driving and come to red light i put it in neutral and then the idle starts to surge from 700/800 to 1k/1.2k, it bounces like this 4-5 times then goes back to normal idle. I cleaned the throttle body and IACV, I heard tps sensor and vacuum lines can be a problem too but i want to know which is more common to start there also if there are other problems that can cause the idle to surge that would be helpful too. Thanks

 

Bleed the cooling system.