Index of all Tutorials
REMOVING AND CLEANING IACV UNIT:
INTRO: The IACV unit is easy to remove. 4 10mm bolts. Reach in at back of engine by firewall on passenger side. No need to remove intake manifold. Pictures are just for illustration. Very easy to disassemble. Make sure you find the plastic piston and spring. This is what needs cleaning.
DETAILS OF REMOVAL:
The connectors have staples. remove the blue connector first. the yellow connector can be removed after you take bolts out and hose off of metal intake tube. make sure you reconnect 3/4 in inch diameter hose and yellow connector first when reinstalling iaa unit. black tie on ficd is reuseable. You will likely find that the aac valve is clogged with carbon mud.(easily comes off carb cleaner). You will have to remove epoxy off brass screw to remove it.(some years dont have this large brass screw). Be careful not to damage threads and slot for screwdriver. The brass screw can tighten or loosen the spring that shuts aac valve. It is best to screw the big brass screw clockwise at first because threads are filled with epoxy. You can then clean the threads and brass screw will unscrew and come off so you can clean the valve.
TESTING ELECTRICAL ASPECTS OF IACV UNIT
Ensure unit grounded properly. The metal contact between the unit and the engine is the ground. A wire from metal part of iacv to engine would provide a second ground. Make sure car is grounded properly too. What is resistance reading between negative battery post and engine chasis. Resistance should be low for there to be good ground.
2 wires from FICD solenoid(blue plug) :
First wire: black from solenoid to connector at front of engine. becomes green at connector and goes to diode(|<). continues green after diode and goes to green/yellow where it splits. one branch goes to slot 45 on eccs unit. the other branch goes to ambient switch which goes to ground when switch is closed.(reads open to gound)
Second wire: Red from solenoid to connector at front of engine.becomes blue after connector and goes to a/c relay.(reads open to ground)
2 wires from AAC solenoid(yellow plug):
First wire: Red/white from solenoid to connector at front of engine. changes to light blue and goes to 113 on eccs unit.
Second wire: red/green from solenoid to connector at front of engine.
changes to brown and goes to positve at fuse box.
(the connector at front also has two wires from air regulation solenoid. blu/red changing to black/yellow and blue/white changing to black. the black wire goes to ground and reads 3.5 ohms)
(the connector is right at front of engine so it is easy to access.. The winding resistance should be 10 ohms for the aac valve/solenoid. you could apply voltage to solenoids to see if they work , also)
My car does not have air conditioning so no point checking ficd.
Testing the AAC(auxiliary air control):
A. Check overall function
1. start engine and warm it up
2. check idle speed- should be 700 -+ 50(if no good, adjust)
3.perform self-diagnosis. make sure code no.43
is not displayed. make sure that throttle sensor is not in
"fail-safe" state.
4.disconnect throttle sensor harness connector
5. if idle speed drops, INSPECTION ENDS.
6.if idle speed does NOT drop, GO TO B.
B.Check Power Supply
1. stop engine
2. disconnect aac valve subharness connector
3.turn ignition switch to "ON"
4.check voltage between terminal "e" and ground.
5. battery voltage, go to 'C"
6. if not battery voltage, check harness connectors, 10a fuse, harness
continuity between aac valve sub-harnesss connecot and fuse
C. Check output signal circuit
1.turn ignition switch "OFF"
2. disconnect ecu harness connector
3. check harness continuity between ecu terminal 113 and terminal "f"
4. continuity should exist
==================================================
General trouble-shooting guide. Not especially helpful in my experience.
TROUBLE SHOOTING (1991 240sx)
******************
HIGH IDLE: 5,8,13,21
UNSTABLE IDLE:
after warm-up:-10,25,2,4,7,1,13,8,3,12,17,18
hunting:-13,25,7,8,10
ENGINE STALL:
Cold-9,25,2,4,7,1,17,19,18
Hot-15,25,,2,4,1,17,19,18,20
On momentary acceleration-9,25,2,4,1,17,19,18
after deceleration-9,3,25,2,4,1,13,17,19,18
acceleration or cruising-25,2,4,1,8,17,19,18
heavy electrical load-6,25,2,4,1,17,19,18
While turning-25,2,4,1,17,19,18
Symptom definitions:
===============
1.ensure fuel pressure within spec
2.perform appropriate test in injector malfunction diagnostic chart
3.inspect throttle body ports and valves for deposits, wear or plugging
4.check for spark using spark tester
5.Check idle speed control circuit.
6.Ensure battery is fully charged and maintains at least 9.6 volts during cranking.
7.check spark plug gap and fouling
8. ensure no vacuum leaks in intake system
9.Check fast idle system.
10.check egr control valve operation
11.Check EGR control valve solenoid operaton.
12. check engine compression
13. disconnect exhaust gas sensor and monitor change in driveability. if it improves, replace sensor. if not, go to 16.
14.Remove canister purge line from intake and test drive vehicle.
15.Remove vacuum hose from fuel pressure regulator and monitor for symptom change.
16.enter self-diagnosis mode 11 and monitor exhaust gas sensor operation
17.check ecu harness connector
18.try a good known ecu
19.Check ECU power source and ground circuit.
20.Check timing belt for proper installation(V6 models)
21.Check throttle linkage operation.
22.Try a known good airflow meter.
23.Check for intake valve deposits.
24.Check engine temperature sensor
25.perform power balance test
Modified by vancouverbc at 1:37 AM 7/10/2007
Modified by vancouverbc at 6:05 PM 8/7/2008
Modified by vancouverbc at 7:22 AM 8/10/2008
1989-1998 240sx TUTORIALS
FACTORY SERVICE MANUAL
Factory service manual2
Factory service manual 1989
Old FAQ
INSTALLS
Pictures of parts
ol lady took mine 
