I'm having a weird idle problem on my 96 GS-R. Basically, it idles normally at about 750 RPM, but after you rev it up in neutral, it drops down to about 1k, revs back up to about 1300, then drops back to 750.

Are there any specific vacuum lines I should check with this symptom? Anything else it could be besides a vacuum leak?

 

i'd say it has more to do with the iacv being slightly clogged with a little carbon. remove the iacv from the backside the mani and clean it with carb cleaner. that should fix the problem

 

Cleaned the IACV thoroughly with carb cleaner, but I'm still getting the same symptom. What is interesting is that the idle itself is fine, but when you rev up, it is hesitant to drop back down. Other than that the car is driving normally.

Could it be the fuel pressure regulator? I messed with it a little bit, the symptom went away for a few mins, then came back.