Where would i locate the IACV on a D16a6...?

 

Honda calls it EACV electronic air control valve..
See:

 

And how do you know if that goes bad or not? And what does the fast idle solenoid do as well as the eacv?.

 

u can tell for sure if the eacv goes bad if there is a surging idle...1000-2500-1000 etc...
You can be sure of that if u slide a thin piece of cardboard to cover the 2 round ports..then if there is no surging thats your problem. As far as the FIV...if it is stuck on the open position..just block off the vacuum port as well as the hose thats running to it...

 

Until u can get a replacement that is