Idle Issue

[nic.brown0627]

Okay so I bought a 98 Civic about 3 weeks ago and for the last couple days I've notice that if I let the car idle for a little while (cold or warm) it will go from idling around 800rpm to 1600/1700 rpm. Also, if you barely touch the throttle the rpm will then start to bounce from 1900 to 2000 rpm for an example it mimics a 2-step kit on a turbo charged engine if you get what I'm trying to say. What should be my first step toward solving this problem?

 

[nic.brown0627]

I took the intake manifold off my friend's y7 which he no longer uses now it works perfectly.

Y8 intake manifold my bad* the Y7s suck (design wise)

 

[s2kver02]

check your IACV and clean it