Page 4 (Updated 03-Nov-2008)
Click To Page: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 INDEX
.
.
.
IACV Idle Air Ctrl Valve
- IACV Overview
- System Parts
- Cleanup
- Idle Speed Adjustment
- Testing the stepper motor
Free Service Manual, Free Download.....see FAVORITE LINKS -page 26- FAVORITE LINKS
________________________________________________________________________________________________________________________
Overview
Idle Control consist of a valve assembly powered via a stepper motor. The stepper motor is controlled directly by ECU, based on various sensor feedback.
Idle assy should be opened & cleaned of the accumulated carbon deposits to stabilize fluctuating idle. Typically this 'needs' to be done once in 60k miles.
.
The assembly is installed with four hex nuts. Open the system. Last part into the intake is paper seal, others rubber o-rings. Add liquid sealant on the paper seal [paper seal not really needed, most probably may be used again]. Clamp the two water tubes, take tubes off (this way there's no need to take all cooling liquid out and bleed air bubbles off).
____________________________________________________________________
IACV Circuit Diagram
Functional Intake/IACV etc picture
________________________________________________________________________________________________________________________
IACV System Parts
.
Stepper motor valve seat assy (rear) and (right pic) seen from valve side
.
.
.
Idle air channel under/inside the intake manifold.
.
.
The air valve actuator can be tested like a thermostat: insert it into a kettle with boiling water and inspect how the valve moves, take out and see how it moves back. If its not working, will likely cause rough cold idle. Note: FSM says this flap is only safety device against hi idle if stepper motor jams open.(FSM; see Favorite Links p.26)
No need to drain coolant: clamp hoses flat tight, and disconnect tubes for testing.
.
.
.
____________________________________________________________________
Throttle Body Zero Adjustment
Zero adjustment screw for throttle body butterfly/axle. This is a stopper screw, and it has to make contact just before the butterfly flaps hit the body.
.
.
________________________________________________________________________________________________________________________
IACV Cleanup
Use any common car solvent in cleanup: some places sell special intake cleaner spray, use gasoline etc.
Nissan FSM warns their mechanics not to open this assy because of possible air leaks, which is surely right:) but with anybody able to open the hood, its very easy task. If problematic leaks arise, liquid gasket sealant will close all leaks. (If hoses do not settle 100% properly after installation, any tiny leak will 'ruin' idle quality: reseat and/or insert sealant.)
For errant idle, check PCV valve malfunction(may also cause excessive oil consumption). Testing may be done with blocking PCV hose for a moment. It may be taken out altogether: block intake side and install a new long hose running down the engine.
Most rubber hoses, if leaking, cause bad Idle.
Some do whole IACV cleanup by squirting cleaner spray into IACV air input hose; needs attached extension hose bit with a small hose to squirt intake cleaner spray in while idling. Surely helps;
- functional operation cannot be verified,
- cleaning is not perfect,
- all soot that is let loose, gets into engine (not too bad).
I would rather do this than leave it undone.
.
________________________________________________________________________________________________________________________
Idle Speed Adjustment
Idle speed (A/T: in "N" position), 7-800 rpm.
Adjustment:
- Turn the Mode Selection SW on the ECU fully CW ( Closes IACV valve completely).
- Adjust engine speed by turning IACV bypass flow adjustment screw (6.)
- Turn back the ECU Mode Selection SW; fully CCW
FSM: Idle Adjustment starts with checking ignition timing etc, then continues to ECU test program III; see Page 21 and FSM EF&EC page 29. All electrical devices have to be shut off, wheels straight on.
------------------------------------------------------------------------------------------------------------------------------------------
See ECU Page 15.
------------------------------------------------------------------------------------------------------------------------------------------
.
.
____________________________________________________________________
Testing IACV Stepper Motor
How to test the stepper motor?
.
.
Connectors and their pins.
.
.
Check also Nissan TSB NTB94-085.pdf; idle fluctuation due to filter.
TSB's see for http://maxima.theowensfamily.com/tsb
Heres one good IAC tech link: http://www.megasquirt.info/ms2/IAC.htm
.
.
.
.
.
.
.
.
James tuneup priorities for the driver: "...what shall be on the morrow: For what is your life? It is even a vapour, that appeareth for a little time, and then vanisheth away."
.
.
.
------------------------------------------------------------------------------------------------------------------------------------------
Click To Page: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 INDEX
