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Discussion Starter · #1 ·
hello, I have 2001 Nissan Altima gxe, auto. I'm having this problem with my idle,at cold startup the idle is about 1600 rpm then it goes down to 1100-1200 rpm in normal temp, it doesn't go down to 800-750rpm used to be. I checked the intake manifold ( no gasket leaks),I clean iacv,inspect the 2 solenoid and adjust the idle but it goes down just to 1200 rpm, check the coolant temp sensor(its fine),tps is starts at .52v to 4.07 v highest in fully open throttle, spray maf sensor w maf cleaner,spray tbi with throttle body cleaner,check cam idle and it idle screw seems it sitting there correctly,so I don't know what to do,any suggestion is greatly appreciated,thanks
 

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09 Altima 3.5SE 6MT Sedan
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Something is making the ECU think 1200 is normal or necessary. How about the coolant temp sensor? O2 sensors?

Have you check for any stored trouble codes?
 

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Discussion Starter · #3 · (Edited)
Btw the car has 88 k miles. Coolant temp sensor works fine, i took it out and starts testing it . The 02 sensors are original when i bought the car brand new ,no engine code or anything.

I do remember it started acting like this when its only 45k miles at that time 8-9 yrs ago
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #5 ·
When i disconnect both wiring to the iacv ,the idle went down to 900rpm, i dont know what does it mean.
 

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It means you need a Consult connected to your care while the idle is reset. Only dealers have these.
 

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The O2 sensor has nothing to do with idle. I was going to say perhaps the throttle cable wires (accelerator and/or cruise control) were too tight and could be causing it. Until, you mentioned that disconnecting the IACV wiring brought the idle lower. So that sounds like an IACV related issue. Can you adjust the idle screw further down and drop the idle, with the wiring disconnected?
 

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Discussion Starter · #8 ·
Its already all the way in ,it stays at 900 rpm with the wiring disconnected and the throttle cables, cruise control are not that tight.

Also When i put the multimeter on the tps lower socket wiring ( i think this the switching?) ,it will read ( in voltage) only when i push the throttle half way
 

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Discussion Starter · #10 ·
It was the brown connector,the one facing upward that makes and change idle high to 1200 rpm.
And the purple connector stays the same at 900 rpm with or without plugging in.ty
 

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Could really only be two possibilities; either the IACV or the ECM. I'm tempted to believe it's the IACV. I do have a curiosity though, how much resistance do you get on the IACV terminals where the brown plug connects to? It also sounds like the ECM is sending a high voltage over to the IACV on the Skyblue wire or there is a constant ground riding on it.
 

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Discussion Starter · #14 · (Edited)
Its 11.9 to 12 ohms
you said ECM sending higher voltage on the iacv, how do i test it and what is the correct voltage? ( engine running at idle normal temp,is it the blue wire and other brown wire or ground?) ty
 

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Sorry I gave you incorrect info on the voltages for the IACV. Here is how is works.

Constant battery voltage is sent on the brown wire. The ECM grounds the other side, the skyblue wire. But that ground should not be a constant ground. That ground instead is turned ON and OFF by the ECM based on what the ECM has been programmed to provide during different engine conditions.

The amount of time that the IACV is doing work (is on duty) is called the duty cycle. The ECM sends a small amount of ground (low duty cycle) during idling. And more ground during wider throttle operations. So if the ECM is sending constant ground then that would be 100% duty cycle. If it was sending ground half the time then that would be 50% duty cycle...a quarter of the time, 25% duty cycle. You get the idea.

Now unless you have a o'scope you wouldn't be able to tell the exact pulse width. There is a test I would like you to do.

1. Disconnect the IACV brown harness.
2. Connect a small jumper wire to the positive battery voltage and the IACV pin terminal - the one which corresponds to the brown wire.
3. Connect a small jumper wire to the IACV pin terminal that corresponds to the skyblue wire. That is the grounding terminal.
4. Start the engine and let it idle. You should get the 900 rpm you had before.
5. Now connect the other end of the grounding terminal to engine ground and see if the idle jumps back to the high level you was previously getting. If so, that confirms that the ECM was sending constant ground on the skyblue wire or that wire is shorted to ground.

By the way, the IACV solenoid should had read about 20 ohms. You are getting about half and that and it is not good. Recheck the resistance reading again to ascertain whether the IACV is indeed bad.

Good luck.
 

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Discussion Starter · #16 · (Edited)
With the engine cold, the IACV solenoid(the one with brown harness) reads only 12 ohms and I checked it 3 times but I will definitely check it again.

I remember after I cleaned the unit , both solenoids work quite all right when I apply 12 volts.

I will try the test tomorrow and double check the value of resistance, thanks

note: Is it during testing, I will get "engine light on" because the brown connector wiring harness is being disconnected with engine on, correct? Also what is the function of the other solenoid(purple connector) for ? Thanks
 

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Discussion Starter · #17 · (Edited)
with the engine warmup, the resistance for the iavc (brown connector) is 17.8 ohms.

I did the test and the idle jump from 900 rpm to 1600-1500 rpm everytime I grounded the pin ( for blue wire) and
engine light came on (p0505) to be expected.
 

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Well the ECM is NOT providing constant ground otherwise the engine would have stayed idling at 1600 rpms. So the ECM must be controlling ground at least to the point where is drops to the 1100rpm range which you mentioned. At this stage, and since you've already confirmed the input sensors are good, then I would have to say it's likely the IACV that is bad. You might be better off first to remove the IACV from the engine and do a thorough internal cleaning of it. Good luck.
 

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Discussion Starter · #20 ·
No changes,same result after I cleaned the iacv,check the 2 solenoids wc are in good working condition ?
 
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