WHAT DOES IT DO?

The AAC valve assists in the idling RPM of the vehicle by controlling air bled into the plenum.

HOW DOES IT WORK?

The AAC valve consists of a control solenoid whose shaft pushes against an opposing spring loaded tapered spool. The movement of the spool allows an air bleed hole to be proportionally exposed which allows extra air thereby increasing the RPM. The solenoid is driven by a pulse width modulated (PWM) control signal from the engine control unit (ECU) at approximately 160Hz. The duty cycle of the PWM signal is varied such that an increase in duty cycle results in an increase in air bleed. If the air conditioner or power steering is activated, the AAC valves duty cycle is increased to increase the RPM which counteracts the additional engine load.

WHAT ARE THE SYMPTOMS FOR WEAR OR FAILURE?

A faulty AAC valve can generate some of the following symptoms:

• Unstable idle RPMs
• Unable to set RPM's at idle
• Stalling on idle
• Hesitation on acceleration from idle.

HOW IS IT MAINTAINED?

The AAC valve can be disassembled and cleaned. Also the spring within the AAC assembly can wear with time and could require replacement.

The AAC valve can also be reconditioned as per the instructions listed here.

HOW CAN IT BE TESTED?

(Courtesy of Phantom)

It is rather difficult to come up with an easy, no-special-tools means of testing this thing, i.e CRO and pulse generator. That leaves physical removal the only easy option. Even then, the only real way I can think of to do any form of test is to blow in it and see if it leaks substantially in the closed as relative to open position. Whilst my target in the recon was to try to eliminate leakage completely, I have no basis for comparison to a new or operational valve...I was simply going on what I thought would be needed to fix it, however I did get an excellent result so I must have been close. In addition leakage is not the only concern, so is the spring tension status. A good spool seal may still lead to poor operation because of this. A good way to see what's going on is to pull it off, block everything temporarily, and visually observe the spool moving under ECU control. With the variation in signal presented, you can quickly gauge if the spring is adequate if for example the spool doesn't reach the taper or is already too far on the taper at these presented signals. This is indeed a difficult one, hence the plethora of such problems I guess. Perhaps only a very keen enthusiast would be willing to do this. At the end of the day all we can do is provide all the information needed and let the individual decide what they can/want to do..

WHERE IS IT LOCATED?

On the end of the plenum closest to the firewall.

	What does it look like? - R33 Series II RB25DET AAC

WHAT IS THE PART NUMBER AND COST?

R33 Series II RB25DET AAC

• Nissan part number ???
• Cost AU$650+??