IAC question45.

[unknown007]

its for a 1993 q45.

well today i tried to see why my car still ildes funny.It goes up then drops to 100-0 and sometimes dies or goes back up to 500 then back down and up to where it's at.On cold crank what rpm should it ilde because mine does at 900-700rpm at cold.I think it's pretty low?

Then i tried to see if the ilder was working so i tried doing a test and got no readings.Back probed then to see what it ohms at and we got from 10-12.2 volts unless were kept touching something else?

Any idea my teacher said maybe it needs to be replaced?Its only because we get no readings.

[Infinitiguy19]

Well honestly the idle of the car should be your least of your concerns because I think you have 3 bad injectors like you said.

You should only set the idle via the IAC AKA AAC valve when: you have cleaned the plenum, TB, Runners and EGR and have 8 good injectors with spark plugs.

[unknown007]

well me and mike did it.at first it was okay but i think we adjusted it when i car was cold maybe?i dunno but looking forward to taking the spider off.

[goody90q45]

I made the 90 minute drive last week through the Sacramento River delta (4 draw bridges and a toll bridge along the way) to meet Berner and try to help him get his Q running a little better. He owns a very nice Q (white with black interior) and it runs much better than what he describes in his posts. We got the engine warmed up and did an analysis with Nissan Data Scan . As I recall it was idling at about 1200-1300 rpm warm so the only adjustment needed was the idle.

Then i tried to see if the IAC was working so i tried doing a test and got no readings. Back probed then to see what it ohms at and we got from 10-12.2 volts unless were kept touching something else? Any idea my teacher said maybe it needs to be replaced? Its only because we get no readings.

well me and mike did it. At first it was okay but i think we adjusted it when car was cold maybe?.....

We did wait until the engine was warmed up to adjust the idle. IIRC when warmed, the IAC was running in the 30's at about 1200 rpm and responded to the adjustment of the IAC screw. When the adjustment was done the IAC was running at 8 and the engine at 700 rpm. I really don't think there's anything wrong with the IAC valve other than it's not been cleaned.

If the idle is a bit low at startup adjust the idle screw to where you think it should be. We may have been at the low end of the ideal 650-750 rpm range with a warm engine so it wouldn't hurt to turn the idle up a bit.

Well honestly the idle of the car should be your least of your concerns because I think you have 3 bad injectors like you said.

Actually only two are bad- one is dead (#3 @ 1.5 ohms) and another is on its way out (#4 @ 19.0 ohms).

.....well today i tried to see why my car still ildes funny. It goes up then drops to 100-0 and sometimes dies or goes back up to 500 then back down and up to where it's at.

We did clean the MAF connector pins (green corrosion) and tighten them and had this same problem after reconnecting. I thought we had fixed the wavering idle. This issue is MAF or connector related and has nothing to do with the IAC valve. Check the MAF connector and MAF pins again and make sure that the connector fits tight. Your connector is missing a small plastic piece but it seemed to be secure on the MAF with the metal clip installed. Do you have a spare MAF available that can be swapped in?

[unknown007]

No i do not.Any way of maybe cleaing it?

The connector is in as far as it'll go.But im cleaning all connectors today couldn't do them alst night got too dark.

I'll check in later.

[unknown007]

How much would a spare MAF be?If u happen to have a spare maybe i can go down and test it?If i have any gas left by the weekend?

[Denver90Q]

Nice tutorial on cleaning IAC valve. I think the Q45 one is the same.

zerothread/251133

[unknown007]

reading it thanks.

[unknown007]

Just 2minutes ago i turned my car on reving dropped and bounced up and down.Put it in drie and gased it a little bit ran i let go and then the car lost power.I looked at the RPM it was dropping from 500 to 100 and back and fourth.If i remember the idle suppose to be 650-750rpm?mine does it at 500 flat now. should i adjust the ilder again?ilders at 500 on cold and warm sometimes 700 at cold.

[Infinitiguy19]

Have you checked an made sure that the injectors are fine at cold and hot temps?

Have you replaced the injectors?

Have you cleaned the Throttle body, EGR, Intake runners, AAC and plenum?

It shouldn't be touched unless the above are performed, other wise your just temporally covering up the the problem.

[unknown007]

Member tight budget right now still.I applied for jobs hopefully will get one so i can get injectors i need them bad.

How do you clean the throttle body?I changed the gasket and cleaned inside.

EGR?Intake runners?ACC?How do you clean the plenum?

I guess all this should be done once i change my injectors to do it all at once?

Man so much work.

I did clean all my connectors today and took off all the corrosion.

I think i need to change the air filter dunno how old it is but i think it's paper or cardboard gotta check.

Well can't spend money anymore gotta get the Q running good now.It's all getting to me.

[Infinitiguy19]

Which connectors did you clean?

There are plenty of threads on removing the plenum and all of the components, Hell Mike did it him self plenty of times see if he will help you or at least give you some tips.

But look up the great write up Mike and many others have mad on removing the plenum.

[unknown007]

Which connectors did you clean?

There are plenty of threads on removing the plenum and all of the components, Hell Mike did it him self plenty of times see if he will help you or at least give you some tips.

But look up the great write up Mike and many others have mad on removing the plenum.

Oh i know where to find how to remove it but cleaning it?it'll say there too i guess.I'll search.

The connectors of the MAF,injectors only got the two fronts the backs i couldn't my engine was too hot still after it sat for like 2hours.

But yeah and the ones by the throttle body

[goody90q45]

I think i need to change the air filter dunno how old it is but i think it's paper or cardboard gotta check......

Did you clean the MAF sensor internally yesterday? A dirty air filter could make for a dirty sensing wire in the MAF and the idle fluctuations you're seeing. There's a current thread on MAF cleaning you should read.

Your IAC was working fine when you adjusted the idle, We watched it working on Nissan Data Scan. You know the MAF connector is clean and tight so pick up a can of MAF sensor cleaner or electrical parts cleaner (and an air filter) on the way to school today and clean it first before pulling out the IAC valve. It's not rocket science and your instructor will be able to show you how it's done.

If you think the idle is a little low make an adjustment. You've done it once and it was very easy. No laptop this time so have someone sit in the car and watch the tach while you work the adjusting screw.

[unknown007]

My teacher said there is not suck thing as cleaning a MAF. Lol i rather do it in the weekend incase i mess up. will check in later.

[Q45tech]

The inside tach is not accurate enough at low rpms to adjust anything!

5% accuracy would be required ------------ the ability to resolve 25 rpm variance.

[unknown007]

Q45tech i wish i understood but i suck with vocab.But correct me if im wrong.

Your saying the difference between the actual rpm and the techometer one if 25 rpm difference??and 5% different?

Learn new things everyday.

[Q45tech]

The highest accuracy in a meter movement is usually at the midpoint 12 oclock position.The lowest position is inaccurate and hard to read 600 vs 700 much less 650 or 625 rpms.

Even with lots of practice my visual guess is often 100 rpms off from Consult at idle.

[qship96]

The highest accuracy in a meter movement is usually at the midpoint 12 oclock position.The lowest position is inaccurate and hard to read 600 vs 700 much less 650 or 625 rpms.

Even with lots of practice my visual guess is often 100 rpms off from Consult at idle.

And how much does it REALLY matter if you idle is set to 600 vs 625 vs 650 vs 699 RPM????

[maxnix]

And how much does it REALLY matter if you idle is set to 600 vs 625 vs 650 vs 699 RPM????

Amount of fuel you burn at idle when mpg = 0.

As low as possible that will still pull all accessories and step off smoothly.

A Boeing engineer of German extraction could sync the carbs on the 2.8L SOHC I6 so well it would idle flawlessly at 500rpm until they went out of sync in just a few thousand miles.

[unknown007]

Im so like lost now!!!

Maybe i need sleep but what i don't get is how am i suppose to fix the idle?clean the IAC?

I somewhat understand that rpm thingy but still lost.

[Q45tech]

With IAC disconnected [electrical] the air flow thru [under] the closed throttle plate and the manual ajustment screw on IAC [zero duty cycle] should be 600 rpm. When IAC is pulsed at 15% the extra air should get to 650 -700 rpm. Ecu corrects IAC % when shifted into drive or ac, elec, ps load.

At 80-100% duty cycle the extra air should be enough to exceed 1300 rpm.

When you are cruising at 70 mph and sudden lift throttle to slow down the ecu slowly drops IAC % from 80% in timed steps to avoid engine stalling as speed decreases. Same with panic braking IAC keeps engine from stalling yet doesn't increase braking distance.

[unknown007]

Ok I get it a lil more now.But what does that say about when i drive and my RPM drops to 100-90RPM and back to 400RPM then back down then 500 then back down to 300 then where it should be?

When i turn me car on with out hitting the throttle as the rpm goes up and begins to drop, it drops to zero and shuts the car off.Happened twice yesterday since i wanted to see how many times it does it.Pretty much until i gas it and hold it for a minute.

[Q45tech]

The ecu requires a certain minimum MAF voltage [estimate of air flow] to CONCLUDE that the engine is running plus of course the rpm signal.

There is one MAF voltage [+- 20% exponential adjusted] that is right for each rpm with the TPS voltage [+- 20% linear].

Abnormal things:like intermitent air leaks allowing air air into engine that is not measured by MAF...............or...............intermitent or bad MAF connections external or inside MAF where the output voltage is WRONG for the perceived situation based on TPS and rpm and outside the +-20% working range [ for barometric and air temperature changes due to altitude or hurricanes or Death Valley].

Intermittent signals from CAS [two separate outputs for 1 and 90 degree signals] where the pulse train suddenly has a drop or missing 90 degree pulses that don't add up with the 1 degree pulses. There should be 90 1 degree signals between each 90 degree signal not 89 or 91.The CAS tells the ecu where the pistons are POSITIONALLY in each 720 degree rotation.