1989-1994 240sx AIV / PAIR valve removal

What do these terms mean?

Pulsed Secondary Air Injection (PAIR) Valve: The PAIR valve sends secondary air to the exhaust manifold, using a vacuum created by exhaust pulsation in the exhaust manifold. When the exhaust pressure is below atmospheric pressure, secondary air is sent to the exhaust manifold. When the exhaust pressure is above atmospheric pressure, the reed valves prevent secondary air from being sent back to the air cleaner.

The valve also works in tandem with a solenoid valve which controls whether it’s on or off:

Pulsed Secondary Air Injection (PAIRC) Solenoid Valve: The PAIRC solenoid valve cuts the intake manifold vacuum signal for PAIR valve control. It responds to the ON/OFF signal from the ECU/ECM. When the solenoid is off, the vacuum signal from the intake manifold is cut. When the ECU/ECM sends an ON signal, the coil pulls the plunger downward and feeds the vacuum signal to the PAIR control valve.

OK, here’s the good news: The AIV is basically useless.* You have two choices: Remove it entirely or simply disconnect one hose. People remove it to free up space. KEEP ALL PARTS as you will need for emission inspections and when you sell car.

*(In british columbia, the aiv will help you pass the idle test. In california it is closed loop during idle so you may not need it for idle test, but keep it for visual inspection).

Here’s what it looks like:

WHY the AIV (PAIR valve) IS A PROBLEM:

If reed valves become gunked up in the AIV unit, exhaust gas and condensation will be allowed to flow into the intake (air box where air filter is). This can cause your cars idle to fluctuate or drop below what it’s supposed to, also can cause slight stumble during acceleration. Deposits from exhaust can coat the MAF element and cause ECU to read the wrong amount of intake air flowing past it.

LOCATION: Only the older s13 will have this unit. Nissan realized it was almost pointless and caused problems as it aged, so they discontinued it in the s14 and s15 lineup. The entire assembly is on the right hand side of the engine (looking from front of car), it’s comprised of hoses, a black plastic resonator, the metal AIV unit, solenoid unit, and black bracket which bolts everything to the car.

EASIEST SOLUTION: Simply disconnect rubber hose that goes from AIV unit to air box. This hose takes air from air filter box and delivers it to AIV unit. Exhaust can not get into air intake system once this hose is disconnected. The AIV unit is now getting unfiltered air which should not be a problem.

TOOLS NEEDED FOR COMPLETE REMOVAL:

Ratchet with small and large extension
10mm socket
Philips-head screwdriver
Flat-head screw driver
Rubber caps to plug up the hoses

Removal instructions:

Hopefully your hoses have little colored bands on them, which will help you IF and WHEN you decide to reconnect them to the solenoid. Make note of this before you disconnect them. If there’s no bands or they are badly faded, make a mark with something so you know where it hooks back up. Take pics of the assembly beforehand.

First you need to unbolt the black bracket holding everything to the car. It’s attached with 3 bolts, 2 above the AIV, and 1 below. The extensions will come in handy here. When the bracket is off, loosen the hose clamps for the tubes going to and from the resonator (2 hoses, 4 clamps). Push the bracket forward to gain easy access to the bolts holding it on. Unbolt the resonator (2 bolts), and pull it off from the hoses and set hoses aside.

To remove the AIV unit, first unbolt it (3 bolts), then pull off the small vacuum line connected to the top. Pull hard to pop it off, it shouldn’t rip on you, it’s a tough little hose. Next, Nissan decided to use a metal clamp type of holder on the hose under the AIV. You will need to twist the AIV upside down or sideways to be able to remove the clip. Stick the flat head screw driver between the part of the clip where it sticks up and twist, pull, and push to loosen it. At this point you can remove it or just slide it down the hose.

Your last adversary is the solenoid, which is held on by one last bolt. Show those hoses no mercy as you pry them off. Wiggle the electrical connector back and forth while pulling to disconnect it. At this point you have 2 roads to take. You can clean the AIV and then put everything back together or plug up everything and leave the AIV off,

To clean the AIV, take off the screws holding its two halves together (be careful, they are easy to strip!). Take apart the reed assembly, carefully taking note how it’s put together, and polish/clean them using steel wool and carb-cleaner/gas. If they are deformed you can bend them back slightly yourself, or buy new ones.

If you wish to leave the AIV out you need to plug up every opening left. Either way you will have to improvise with materials around your garage, or you will have to take a trip to the hardware store to find stuff.

• Red plugs into the bottom of the solenoid (vertical).
• Blue plugs into the top of the solenoid (vertical).
• When reconnecting the AIV its hose will have no color, it plugs into the side of the solenoid (horizontal).

For the exhaust hose; you can plug it up with a bolt or some other stopper. I reused some of the clamps to make sure it wasn’t going to budge. Don’t worry about it shooting out of the hose, there is very little pressure in the exhaust, just make sure none of that exhaust is being vented into the engine compartment. The clean way to do this is to weld up the opening where the metal tube connects to the down pipe, but a bolt with some JB Weld should do the trick.