S13 Idles at 3 different stages

[miklos]

My car is idling at 1,000 rpm when warm. Cold idle is lower and varies 500-700rpm

When I am driving--as soon as I release the gas pedal--sometimes the rpm will drop to 500rpm.

I changed the fuel filter and pump.

I looked thru the FSM and it says it could be

MAF
TPS
CTS
Knock sensor
Crank angle sensor
FPR
EGR

Which would be best to look at?

[Jesse SR20]

IACV

Any air pockets in the cooling system and fuck with your idle when they get stuck in the IACV. Or if the IACV malfunctions, same thing.

I'd bleed all the air out of the cooling system. Check for leaks.

If that doesn't do it, remove and clean out the IACV. Or replace if you suspect it's no longer functioning properly.

[miklos]

The idle only drops down when I take my foot off the gas and it's above 2,000 rpm.
So whenever I decelerate [and not using the brake pedal] it will drop to 500 rpm.........then sometimes stopping at a light it will just shut off.

After checking the Egr and changing the TPS; I unplugged the IACV and now when I push in the clutch to decelerate---the idle floats down to 700rpm.

So people are saying I don't need the IACV unless I want the AC to work. It now idles about 700rpm after driving under load; but once in awhile it may go to 500rpm