R33 Idle Problem

[skyrex4]

Hi

My 1995 GTSt has developed an irregular idle of between 500 to 800 rpm.

At cold starts it idles fine above 1000rpm, however, after a minute or so , the above would start to happen.

Once it has been driven on the freeway for a some time and come to a stop, it will idle fine at 700 to 800rpm. Once warmed up, it has only a few times idled irregularly.

A review of same topics on this site have suggested to clean the AFM, clean AAC, clean idle control value , clean IAC & check for leaks.....thanks for your suggestions.

I have recently had a new AFM installed and it ran fine for months....so I do not think it is this and I have checked for leaks.

Can someone advice what AAC and IAC are abbrevations for? I can then look to clean them.

What I cannot work out is why sometimes it will idle fine and other times irregular??????? If something need cleaning, I would have thought the idle would be irregular all the time.

Would it be an electronic issue? What controls idle speed?

Cheers

[GTSBoy]

AAC Auxiliary Air Control (Valve).

IAC Idle Air (Valve)

Used somewhat interchangeably. Not strictly the same thing depending on what car you're talking about. But close enough for our purposes here. IAC is the idle control valve which is driven by a solenoid from the ECU. It's on the back end of the plenum.

They get full of the usual black crud that you find elsewhere in the intake system. But in this case because it's a metering valve with small passages that is supposed to offer fine control of air flow, it matters if it is clean or cludged.

The valve is obviously able to open across a certain range of openings. If it is sticky in one spot but not another, then it may cause you trouble when it needs to be that far open, and will not cause trouble when it needs to be further open (or perhaps closed).

[KiwiRS4T]

Look in the DIY section for help with how to clean.

[skyrex4]

Thanks for your replies, I will have a look at it and give it a clean