hey guys my car idles at about 1400 and i cant get it to drop.I have 3 iac valves i cleaned them all with wd-40 and i checked them with a multi meter to make sure they were good.Turned out they were all good so i went to install them in my car one after the other and i couldnt get the idle to drop.This is the procedure i did let the car warm up,unplug the yellow wire screw the bolt clockwise to drop idle connec the yellow wire back and it wont drop.Itdrops a little bit to about 1200 but thats it wont go any lower.I even bought new connectors and soldered them on and no change.My next step is to check for vacumm leaks AGAIN but i doubt its that because last time i checked i had n leaks and my car runs perfectly fine all i need is for the idle to drop.Any ideas on what it could be?Thank you

Are these all the vacuum lines on a 300zx?

or these to make it easier to read?:)

Have you done a boost leak test?

robomatic12 wrote:Have you done a boost leak test?

no i havent would it work on a non turbo?

Yep, will show you where the vacuum leaks are.

Manual or automatic?

What's the TPS output voltage? 0.40 VDC is a good number.

Checked the Air Regulator? I did a heated throttle body by-pass, also deleting the length of tubing that heats the Air Regulator and now once the engine is warm the idle doesn't drop unless the car is in gear and fully stopped with my foot on the brake pedal, but if the TPS output isn't set correctly, the idle can only drop so far.

If the TPS output voltage isn't set correctly, an automatic transmission my shift roughly/late or hunt OD lock-up and fuel mileage will suffer.

Lots of good info here:

http://www.google.com/url?sa=t&source=w ... IyQqVvpyeQ

my z is manual the tps was set to 45 and the timming was set to 15 .Ever since i owned the car i cant get the idle to drop i think the connnections for the iacv might be cut somewere in the wiring harness im going to check if the computer is sending signal to the connector.I went to a mechanic and he told me it wold cost me $80 for a diagnostic + whatever the issue is he is a z mechanic he knows what hes doing but it gets me mad that i cant figure it out myself

Take a look at this websited sdkid123 hopefully this helps you out

http://s95014253.onlinehome.us/63104/157335.html

^great site there is a couple of very useful write ups on there... Let us know if you have any other questions

One quote:

Air Regulator:
The purpose of the air regulator is to raise the idle during engine warm-up by letting additional air to enter the intake. Symptoms of the air regulator going bad are either a low unstable idle during warm up or constantly high idle. The regulator consists of a bimetal-activated shutter that closes after ~5 min of engine operation and cuts off the airflow.
Note: It's normal that the shutter is only partially open at room temperature.
Check the resistance between the pins in the connector. It should be ~75 Ohm. If not good then replace the whole regulator.
Another problem could be that the regulator is clogged, causing the shutter to stick.

TPS output voltage has a big direct effect on idle speed and its' connector needs to be disconnected and reconnected with the engine running in order to register a new "throttle fully closed" output voltage in the ECM, after making an adjustment. Mine actually is set to 0.38 VDC.

Thanks for your help but i have 3 iac valves and i took them all apart and cleaned them with wd-40 none of them want to work which is the wierd thing

GOOD NEWS i founf a air leak! the hose the goes from the air regulator to the black tube on the plenum had a crack and was leaking air im hoping whe ni replace the hose ill be able to adjust my idle

heres a pic of were the crack on the hose was (look in the purple circle)

Sorry I don't have a simple answer, even though it will be something simple in the end. When my IAC finally does close, seated in the I can hear the click, before the idle speed starts to drop.

My understanding of the mechanical and electrical input/output controlled factors that control or affect idle speed:

- engine temperature as determined in part by the thermostat, and detected and communicated to the ECM
- total air flow through the throttle bodies and AAC/FICD/Air Regulator, and as detected by the MAF and communicated to the ECM, barring any manifold vacuum leaks
- throttle body cleanliness, and accelerator and cruise control cable tension/lubrication as they relate to consistent throttle plate closing and TPS readings communicated to the ECM
- engine timing as determined by CAS adjustment and KS sensor input to the ECM
- alternator, PS and AC load on the engine
- the idle speed adjustment screw, provided everything else is correct

Here's to hearing about the fix for your problem.

sdkid123 wrote:GOOD NEWS i founf a air leak! the hose the goes from the air regulator to the black tube on the plenum had a crack and was leaking air im hoping whe ni replace the hose ill be able to adjust my idle

heres a pic of were the crack on the hose was (look in the purple circle)

Clearly a step in the right direction!

I'm really glad you found the leak hiding back there!!! You would have paid someone millions to find and fix.
I actually made a smoke tester from a transfer pump and a cigar. harbor freight special 10bucks lol.
I could not set my idle air control valve either. Tried and tried. I found 2 leaks before the mass airflow and two broken hoses after the throttle bodys. Now her idle isn't 1500 and jumping anymore she's purrringg at 850
I'm doing the boost leak test with pressure tomorrow to see if shes good.
It's amazing how these cars even have one small leak and they run like hell lol.

Also if that's your engine pulled delete that egr valve ! That will cause you some issues later. Also a pain in the butt to get to when the engine is in the car.