So I have a 1995 Maxima with over 211K miles with idle issue. So when the car is cold the car seem to idle fine. Also the car still runs fine when I'm moving even on the highway. However once the car warms up, the car would idle at 400-500rpm in drive when stopped and it's shaking. It seem to idle better in neutral when stop around 600-650rpm. Also if I let go of the throttle at 40mph or less the rpm would quickly drop from 2000rpm down to 1000rpm or less. It doesn't do it all the time but it started doing this more frequently over time. It's been like this for about a year, and the issue since to be getting worse as in the idle is lower and rougher. The check engine light came on recently and it's a P0505 Idle Control System Malfunction. I was told to first try cleaning the Idle air control valve as it's probably gunked up. I've already cleaned the maf sensor and throttle. However, the idle air control valve is cramped in the rear. Can I first try cleaning the idle air control valve without removing it? I was thinking to disconnect the air hose that goes to the idle air control valve and spraying throttle body cleaner in there. Or is it necessary to removal the Idle air control valve to clean it?

Remove it, take it apart and clean it thoroughly. Clean the TB and MAF also.

I would remove it if you want to do it properly, it shouldn't be too difficult.

Removal is straight forward and takes less than 5 minutes. Why take shortcuts?

ABSOLUTELY!

And make sure you have a NEW OEM REPLACEMENT GASKET after cleaning and reinstalling. Part Number: Nissan 23785-AD100

Tighten uniformly in a diagonal cross pattern for best results

The unit contains several small and delicate parts..

You don't want the small parts to fall down and get lost.

So I will remove it to clean it out. Jvg you mention there's small parts that can get lost. From my understanding after removing the valve (whole triangular piece) I still need to remove 3 screws on the inside of the valve to take off a cover. Is there something else I should know or I'm missing?

Nope. That's about it. Pretty straight forward.

It's simple more than likely the exhaust EGR line port is clogged with exhaust deposits.