Rough Idle when car is stopped but fine when coasting???

[MOscapinski]

I have a 1990 Nissan 240sx with a few upgrades but a lot of new parts including a new engine, MAF, injectors, etc. When my car is stopped, the idle goes from 500 to 800 rpms and it never stabilzes, I have been dealing with this issue for some time but recently I noticed if I'm driving and I put the car in neutral the idle stabilizes around 700-800 rpms until I come to a stop then it goes up and down again. Any suggestions?

[SOHCSE]

Mine did the same thing. I removed the PAIR valve and it cleaned right up

[MOscapinski]

What is the PAIR valve and where is it located? What things should I be looking for when I clean it?

[SOHCSE]

This is what you are looking for. I removed mine completely. It's a pretty easy job.

PAIR/AIV removal

Sometimes this is called AIV