Help with bad idle, how do I clean the IAC?

Got questions about your Infiniti? We're here to help, and it's FREE!
kotex
Posts: 22
Joined: Mon Oct 28, 2002 4:28 am

Help with bad idle, how do I clean the IAC?

Postby kotex » Tue Aug 26, 2003 7:37 am

First off, I am a mechanical moron but I can follow directions well. How difficult of a job is it to remove the IAC from my 94Qt and clean it? Does it have to come off to get cleaned? I am having some idle problems and have removed and cleaned the MAF as is suggested in many posts (connection was fine). Throttle body has been cleaned within the last 3 months. Fuel filter is about 10 months old and I only run 93 octane from Chevron. BG44k is put into the tank after each Mobil 1 oil change at 3k miles. I would check the CAS but I don’t know where it is or what it looks like. How would I go about cleaning the CAS and does anyone have any pics of it?

My car is idling so badly that sometimes it just shuts off altogether. It drives great sometimes and my gas mileage in town is still about the same (15-16mpg). The bad idling is intermittent but is much worse if the car has been sitting in the Florida sun for a few hours. If I leave it in park and rev the engine up to about 3750-4000 RPMs I have a better chance of getting it to duplicate the bad idle if this mean anything.

Also every now and again it will bump and lurch while I’m driving but not if I am applying gas. Only if I am coasting and trying to maintain a certain speed will she lurch. A tap of the gas pedal seems to cure knock her back into shape.

Any ideas? Fuel pump? Fuel regulator? Injector? Bad coil (new OEM plugs by the way)? Could it be as simple as cleaning the IAC and CAS? Maybe a new MAF?

I’ll stop babbling and let someone help. Thanks fellers!


forecast
Posts: 256
Joined: Mon May 05, 2003 6:44 am
Contact:

Postby forecast » Tue Aug 26, 2003 7:37 am

The CAS - crank angle sensor - tells the computer the angle of the engine - where it is in the rotation. it an electrical part that effectively replaces the distributor. It's located to the front of the RightHand (driver's side) exhuaust cam. This isn't a part that gets dirty usually, and malfunctions with it are normally reported by the computer fairly well.

I suspect your IAC (also called AAC) valve is either plugged or disconnected. Check the connector first. If it needs to be cleaned, it can be pulled off by removing the four bolts on the back of it.

However, the symptoms you describe really could be any number of the items you list, esp. the MAF.

Fuel pressure problems usually cause drivablity symptoms, low power under acceleration and such.

Ignition problems (except timing) are also more often across the spectrum - problems at all rpm's

I might suspect the MAF only because you report ocassional hicups when driving.

nuQ
Posts: 1661
Joined: Thu Jan 23, 2003 1:39 pm
Car: 2003 M45.
2009 Dodge Caliber SXT
Location: Bethlehem PA

Postby nuQ » Tue Aug 26, 2003 7:37 am

Had very similiar problems a few weeks ago. Turned out to be the MAF. Sprayed carb cleaner in, a really cleaned the connector, rubbed the metal tabs down a little, used bulb grease and made sure the connection was tight. Also looked to clean the TB but found that to be almost spotless!!!! Could see the brushed aluminum housing inside perfectly. Sprayed a little more cleaner in just to be safe, really tried cleaning the "flap thing" and haven't had any more problems. If any of this helps, but it sounds like you did, pretty much the same thing. jeff

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

Postby Q45tech » Tue Aug 26, 2003 7:37 am

"the "flap thing" ..........the butterfly valve.

Idle rpm changes [with age/dirt] are slow and progressive. Brand new the space under the butterfly valve and the mechanical air bypass [what the screw on IAC adjusts] in the IAC provide 90% of the required idle air flow. Probably divided 50/50 between the two paths. The IAC adds air after the butterfly valve.

The ecu controls a solenoid in IAC that adds puffs of air to control the idle speed. This should add 10-15% more air. When the AC is on this might increase to 30-40%. When the alternator load is heavy this might be 20%, when the engine is loaded in a low speed parallel park this might add 20%............generally 40-45% is as high as you see regardless of extra load.When you are traveling at 60 mph and get off the throttle the IAC duty cycle may be 70> 60 >50% so the engine doesn't die when the throttle is suddenly closed.An 80% duty cycle on IAC may result in a 1200 rpm idle.

The IAC is tested with Consult: 0% idle speed =550-575 rpm, 20%=675-700-725 rpm, 80% =1100-1200 rpms.Hopefully you can see the effects of a dirty IAC, the dynamic control range of the ecu as to idle speed or slow down speed or load changes is compromised.

Cleaning the throttle body is only half the equation! The IAC gasket always fails on removal have a spare on hand!

User avatar
Jesda
Posts: 39665
Joined: Mon May 05, 2003 1:50 pm
Location: THE D
Contact:

Postby Jesda » Fri Oct 15, 2004 9:33 pm

So, where is the IAC and how do I clean it? Does it have to be removed?

-Jesda

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

Re: (Jesda)

Postby Q45tech » Sat Oct 16, 2004 1:01 am

It has to be removed and disassembled and cleaned of the dirt that has passed thru the air filter and built up on the tiny valve [cylinder and bore] and in the bypass screw chamber.

Careful the solenoid rod and bore valve is spring loaded to make sure the valve snaps closed when solenoid duty cycle is complete.

Think of the pick tools a dentist uses to clean teeth after the spray solvent soaks.......don't submerge the solenoid or the unit.

Exercise the solenoid with 12 volts to check function.

Careful removing the valve from the expensive hoses, a cracked hose will mean plenum removal to replace!

User avatar
Jesda
Posts: 39665
Joined: Mon May 05, 2003 1:50 pm
Location: THE D
Contact:

Postby Jesda » Sat Oct 16, 2004 1:38 pm

Is a dirty IAC possibly why my Q ran so well for 300 miles after Seafoam (through the brake booster) but then got worse again? The manual refers to an AAC, same thing right? On the back near the firewall?

User avatar
gniknave
Posts: 4761
Joined: Wed Aug 25, 2004 10:25 pm
Car: 2000 Audi A6 2.8 Quattro
2008 Honda Civic EX (Sedan)
Location: Newport, Kentucky

Re: (Jesda)

Postby gniknave » Tue Oct 19, 2004 1:08 pm

I'm hoping to see a response to the location of the AAC valve. I think it's the same thing Jesda is saying (near the firewall but I'm curious too.

User avatar
Jesda
Posts: 39665
Joined: Mon May 05, 2003 1:50 pm
Location: THE D
Contact:

Re: (gniknave)

Postby Jesda » Tue Oct 19, 2004 3:40 pm

I did locate it, the factory manual calls it an AAC.(http://nicoclub.com/zerothread?id=82862&page=2)

The manual reads "The ECU actuated the AAC (Auxilary Air Control) valve by an ON/OFF pulse. The longer that ON duty is left on, the larger the amount of air that will flow through the AAC valve."

Its attached right behind the plenum halfway between the driver and passenger side toward the firewall. It also has a hose going out the bottom and a metal cylinder coming out the side. I removed the four bolts holding it on, then unclamped the hose and very slowly and carefully pulled the hose off.

I then used a philips head screwdriver to remove the metal cylinder and sprayed carb cleaner in every nook and cranny I could. Per Dennis' instructions, I did not soak it.

I really cant tell if it made a difference in idle quality, because my particular problem is caused by a bad MAF. It has a plastic idle adjustment screw on it that most folks suggest not messing with, since its hard to get the idle right. But I needed to get to school and the company van wasnt always available to me, so I upped the idle by loosening the screw to keep the revs up. I'll have to go through the trouble of precisely trying to set the idle once my new (used) MAF arrives later this week. Some photos are attached.









-Jesda

User avatar
elwesso
Posts: 34280
Joined: Sun Feb 23, 2003 4:52 pm
Car: 94 Q45t 5 speed, 2007 BMW M Coupe, 2007 G35S 6MT
Location: Indiana
Contact:

Re: (Jesda)

Postby elwesso » Tue Oct 19, 2004 4:20 pm

jesda.....

Set the idle so that its at 650-700 RPMs... The idle will always be low until you clean the plenum... SO get it where its liveable, and then precision will come when the plenum is spotless......

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

Re: (elwesso)

Postby Q45tech » Wed Oct 20, 2004 6:27 am

WRONG, the more the bypass is used the less dynamic range the ECU has to control idle and cruise sudden lift throttle........using too much bypass will make weird things happen at cruise.

Set it 2.5 to 3.5 turn out and live with the idle speed result or fix the dirt problem

SOCAL91Q45a
Posts: 403
Joined: Sat Aug 16, 2003 2:28 pm
Contact:

Postby SOCAL91Q45a » Tue Mar 01, 2005 7:39 pm

OK - so whos cleaned it and how did it do?

Whats a new IAC /ACC cost ?

User avatar
Jesda
Posts: 39665
Joined: Mon May 05, 2003 1:50 pm
Location: THE D
Contact:

Postby Jesda » Tue Mar 01, 2005 8:00 pm

I think its fairly rare for them to go bad. Joe at Scottsdale sells them (www.everythinginfiniti.com). When I removed mine for cleaning, not much changed. It wasnt that dirty.


Return to “Infiniti Online Mechanic”