This post borrowed from here

TBI Component Listing & Locations

This is a component listing of the vg30i and z24i TBI system. Both engines use the same components shown except the z24i air boxes are smaller. All pictures were taken from my 1989 vg30i and spare parts collection.

This is more of a reference page than a straight read and will not be all the information you need On each particular part put it will be enough to get most people going in the right direction and will make for great reference the next time someone says is there a way to adjust the thingamajig and where is it?

OUTSIDE THE AIR BOX

Air box & Air box Lid-

Houses the air filter, Crank case filter and Hot air pickup control module. It can whistle, rattle and let unwanted debris past the filter if not secured all the way; 5 latches around the edge should be springy and fir and the 2 wing nuts should be finger tightened 2-3 rotations further once they touch the lid. Over tightening will strip these very easily.

 

Idle Up Solenoids-

Under the driver's right side of the air box are 2 solenoids that open a passage around the throttle body to increase idle speed when the A/C compressor turns on or when there is an increase in electrical load. I believe the right one in the picture is for the compressor and the left is for electrical. If your Idle drops when under electrical or A/C usage chances are the Idle up adjuster needs to be turned. Check wires and plugs too before announcing them as broken. If you pull them out they should have a rubber tip, round is good cone shaped is worn and if there is metal showing on the tip it needs replaced.

 

Idle Up Adjuster-

This slotted screw head controls how much air is allowed to bypass the throttle body. Counter clockwise increases idle-up (It may tak a full rotation to make a noticeable ajustmet). It should be set so that there is about 50-100 rpm increase when the compressor turns on or electrical load increases (blower motor, rear defroster etc...)

(Another picture of the Idle up solenoids and adjuster can be seen in a following section about the actual throttle body.)

 

A B Valve-

Short for Anti-Backfire Valve this valve Reduces backfiring during deceleration.

 

Crank Case Breather Hose-

Allows un-regulated Ventilation of the crankcase so that heat, oil gasses and (if) any combustion gasses enter the crank case has a way out. This can reduce stress on the oil and prevent valve cover gasket failure. It vents into the intake and directly into the manifold thru a PCV valve (regulated) for emissions purposes and to keep cleaner air circulating thru the crank-case. Older vehicles just had a vent and maybe an external screen or filter over it.

 

Hot Air Vacuum Motor-

Opens the hot air pickup door in the intake to allow air from around the exhaust manifold pickup (also called stove pipe) into the intake and then closes it as the air box heats up. It can become jammed; restricting your intake and keeping hot air flow at all times or fail so that it never opens, a bad vacuum line can do this too. Check your Vacuum Control too if you suspect problems.

 

Hot Air Pickup Hose-

This is an insulated high temp hose that delivers hot air form around the exhaust manifold. When old it can become brittle and tear letting cooler air in or the insulation can collapse and restrict the flow of hot air.

 

Idle Screw-

Head points divers right, Adjusts engine idle speed; clockwise is faster. 750-800 rpm is typical the typical setting but anywhere from 700-900 is also acceptable. (Measurement is with a warmed up engine & all accessories turned off)

 

Fast Idle Screw-

Head points skyward and is often mistaken for the normal Idle Screw. When the engine is cold the Fast Idle Cam increases the idle for faster warm-up. This screw sets the fast idle speed which should be between 1,000-1,200 rpm set depending on how cold your climate is.

 

INSIDE THE AIR BOX

 

Hot Air Pickup Control-

This little vacuum control device shuts off when it heats up. If your hot air door is still open after full warm up on a warm day (stick your hand thru the intake you can feel it) then it is either stuck or needs readjusting. It comes form the factory with a hard loc-tite like seal around the screw and the tab next to it (be careful, it's sensitive). Counter clockwise makes the vacuum shut off @ lower temps, try your adjustments in 1/4 turn increments if you feel you must tamper with it. Staying open too much restricts intake air-flow and robs power from "hot-engine hot-air-mixture" and too little makes warm-ups longer and may make richer smelling exhaust from "cold-engine cold-air-mixture" The goal is (hot as in operating temp);

 

Crank Case Ventilation Filter-

This catches the oil and particles that come out of the vent so that it doesn't gum up your throttle body or air filter.

 

Injector Cap-

The injector cap covers the injectors and holds the Injector Retaining Ring down. It has a Vent on each side and no these vents are not just to cool the injectors. They are to allow air to the Mass Air Flow Sensor. Unlike other vehicles where the MAF is directly in the air-stream the Nissan TBI has separate channels that run beside the throttle body.

 

Injectors-

Nissan TBI injectors pulses just the drivers right injector @ idle when cruising or as fuel demands increase both injectors will begin alternating pulses.

Don't tamper with these, if they fail they cost allot to replace new or remanufactured. Problems can include leaky, clogged, incorrect resistance and a whole slew of other diagnostics that should be found on another thread(s). You can remove bad ones by pulling firmly on the wires. Remove good ones only by taking the throttle body halves apart and using a hollow point punch or socket to press them out w/o damaging the injector nozzle.