There are roughly 4 idle control valves

Idle Adjustment Screw - The IAS is located on the passanger side rear of the intake manifold. It looks like a large flathead screw. Turn it either way to bump idle rpms down or up to suit.

IACV - Air Regulator (Idle Air Control Valve)- The IACV is an air regulator valve. It's job is to provide your fast idle when the car is cold. The valve consists of either a wax or bi-metallic spring temp. sensing peice and a spring. When the engine is cold the valve is open and thus air bypasses to raise the idle. When the engine is warm the valve closes to drop the idle.

IACV - FICD - The IACV-FICD valve allows air into the motor when the a/c system is on to compensate for the added strain of turning the compressor. This will bump the idle up if working properly.

IACV - AAC - The IACV-AAC valve is an ECU controlled unit that runs off of a duty cycle set by the ECU. The valve operates in an ON/OFF/ON pattern. The greater the "ON" signal, the greater the amount of air that enters the valve (and a higher idle as a result).

* You can test the connectors for resistance to determine if the valves are working correctly. Unfortunately I have only the 93-98 MY specifications on hand. Let me know if you need them

this thread is off to a good start, i put in a vote for someone to write up a how-to to fix idle problems associated with the IACV-AAC and AIV valves (with pics ). That should cure about 3/4 of the engine problems on this board lol.

I will be the first guinea pig, and take pics of the AIV cleaning if you want, since im going to do that today. I can do the IACV-AAC too with pics but would need someone to walk me through it since im kinda uneasy about taking off my intake manifold to get to it.

Nismo_Freak wrote:Idle Adjustment Screw - The IAS is located on the passanger side rear of the intake manifold. It looks like a large flathead screw. Turn it either way to bump idle rpms down or up to suit.

From what I have read, you also have to disconnect the TPS harness before adjusting idle with this screw.

Is this true for the SOHC models as well? The FAQ gave instructions on adjusting idle for the DOHC model only. I tried to adjust the idle today, following the instructions for the DOHC engine, and had no luck. It seemed to have no effect. I was wondering if the AAC valve was defective, since the IAS is attached to it. maybe the TPS sensor is defective as well-the idle didnt drop all that much when i disconnected it. Any help would be appreciated, thanks!

p00t wrote:i put in a vote for someone to write up a how-to to fix idle problems associated with the IACV-AAC and AIV valves (with pics ).

I need that as well:help

Chingon wrote:I need that as well:help

Same here :help

ok everyone. i can see we have a definite need here. let me dig up a copy of the basic inspection procedure. this is in every single nissan fsm. the only differences are specs and a few little equipent changes(coil on plug/dist, tps/etc,port efi/tb efi,etc). give me a couple days to get it typed up for ya(sorry i am very busy at job working on cars for peanuts).

I like to know where the location of all the idle control valves are described in the first discussion

Can someone please post pic or describe them

when my ac comes on it bogs to 550 rpm normal idle is 850

ok here is basic inspection for 94 sentrai will try to get one for obd2 as wellalso i will post how to enter self diag modeeventually i will try to get individual components on here

IDLE SPEED/IGNITION TIMING/IDLE MIXTURE RATIO INSPECTIONI.perform diag test mode II(self diag results) A.ok, go to 2 B.ng, repair or replaceII.check and adjust ign. timingIII.check and adjust idleIV.check heated oxy sensor A.ok, inspection end B.ng, check ho2s harness 1.ok, check co% a.ok, replace ho2s b.ng,check emission control parts 2.ng, repair or replace harness

START

visually check the followingair cleaner clogginghoses and ducts for leaksegr valve operationelectrical connectorsgasketsthrottle valve and throttle position sensor operation

start engine and warm it up until water timp indicator points to the middle of gauge.ensure engine stays below 1000 rpm

open engine hood and run engine at about 2000 rpm for about 2 min under no load

perform diag test mode IIif ng, repair or replace as necessaryif ok, continue

run engine at about 2000 rpm for about 2 min under no loadrace engine 2 or 3 times under no load, then run engine for about1 min at idle

select "ign timing adj" in "work support"touch startor without consultturn off engine and disconnect tps harness connectorstart engine

race engine 2 or 3 times under no load and then run engine at idle speed

check ign timing with a timing lightorange notch is zero

check idle speedread idle speed in "ign timing adj" in work supportor without consultcheck idle speed(with tps disconnected)if ng, check iacv-aac valve, harness, and ecmif ok, continue

race engine 2 or 3 times at no load

see "m/r f/c mnt" in "data monitor"run engine at about 2000rpm for about 2 minutes under no loadmaintaining engine at 2000rpm under no load(engine warmed up). check that the monitor fluctuates between lean and rich more than5 times during 10 seconds.or without consultset the "heated oxygen sensor monitor" in diag test mode IIrun at 2000rpm under no loadmaintaining 2000rpm under no load, check to make sure that the red led on the ecm or the malfunction indicator lamp on the ip goes on and off more than 5 times during 10 sec

END

check ho2s harnessturn off engine and disconnect batt ground cabledisconnect ecm smj harness connector from ecmdisconnect ho2s harness connector and connect main harness side terminal for ho2s to ground with a jumper wirecheck for continuity between terminal no 19 of ecm smj and body groundshould have continuity

reconnect ecm smj

connect batt ground cableselect "eng coolant temp" in "active test" modeset "coolant" to 20*C or without consultdisconnect engine coolant temp sensor connectorconnect resistor(2.5KOhms) between terminals of ect connector.connect batt ground cable

start engine and warm it up untill water temp indicator points to middle of gauge

race engine 2 or 3 times

check co%(less than 5%)touch "back"or without consultdisconnect resistor from ectconnect ect connector

if ok, replace ho2s, and star overif ng, continue

reconnect ho2s

check fuel pressure

check maf sensor and circuit

check injector(s) and circuit(s)clean or replace as necessary

check ect sensor and its circuit

check ecm function by substituting another known good ecmecm may be prob, but is not likely(yeah, when they are new)

94 sentra 2.0on board diag. sys function diag mode I diag mode IIign on/engine stop bulb check self diag resultsign on/engine running malfunction warning ho2s monitor

turn key to on(do not start)now in bulb check(normal)start enginenow in malfunction warning(normal)

key onturn diag test mode selector on ecm(little plastic flat head screw) fully clockwisewait at least 2 secturn selector fully counter clockwisenow in self diag results(reading diag trouble codes)

start enginenow in ho2s monitor(checks o2 fluctuation)

turn fully clockwisewait 2 secturn fully counter clockwise

END

note:switching modes is not possible with engine runningwhen ign. is switched off during each mode, and then turned back on after ecmcompletely loses power(can be up to 24hours but should be like 20min), diag will return to test mode Iturn back diag test mode selector to the fully conterclockwise position whenever vehicle is in use

(the reason for the last note about when vehicle is in use is a secret functionof nissan ecm's of this era. any degree of turn clockwise without engagingdiag test mode raises the idle slightly. in other words you can turn up your idle by turning test screw slightly clockwise, but not far enough to go into test mode.)

bulb checkself explanatory

test mode I with engine running(normal engine running condition)mil and led on ecm should now be offif on, read code

test mode II engine not runninglong blink is first digit(tens)short blink is last digit(ones)

test mode II engine runningred lamp on=leanred lamp off=richcan use mil as wellif stays on or off=in open loop

Nizmo always willing to help someone out

Thanks

Do these instructions work for an S14 as well?

My idle has been different for the first time since I had to get my engine decarbed back in December. It used to idle at abt 650 now it seems as though its idleing at about 850. Anyone know why this could be. The reason I have to get it decarbed is because the car wouldn't start, though, I could here the starter working but the engine wouldn't turn over so I had to get it hauled in. My mechanic said two of the valves were stuck in the open position and it was causing a loss of compression so the engine wouldn't start. They cleaned the engine and fuel tank with a kit by 3M. Ever since then I've noticed that the idle has been higher. Of course it idles high when its cold but the idle doesn't drop as much when it warms up and the idle drops when I turn my headlights on and it drops to the same level it used to idle at before. Though, before it seemed like when I turn my headlights on the idle would actually go up. Though, I do know the idle is high now. Also, my gas mileage has dropped for the first time by 1-2mpg. Used to my gauge would start to go down at 174miles now its starting to go down at 160. Any ideas on this?