How to adjust idle speed of a 90 Nissan 300ZX? - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 9 (permalink) Old 01-09-2009, 02:38 AM Thread Starter
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How to adjust idle speed of a 90 Nissan 300ZX?

How to adjust idle speed of a 1990 Nissan 300ZX Non-Turbo?

Currently, the car's idle speed is running at about 500 rpm which is too low. I want to adjust it higher idle speed to about 1,000 rpm.
Please give me detail instructions. Thanks!
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post #2 of 9 (permalink) Old 01-09-2009, 03:17 AM
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Re: How to adjust idle speed of a 90 Nissan 300ZX?

Here is a link to the FSM. Make sure you have an accurate method to determine RPM. the stock tachometer does not count. Many timing lights have the ability to read RPM. The proper base idle is around 750


Idle Adjustment

-Jason

90 300ZX TT
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post #3 of 9 (permalink) Old 01-09-2009, 12:14 PM
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Here is the best way....

You will need a digital voltmeter....And by the way the stock Tach is fine...
First locate the TPS sensor on the drivers side throttle body. Now you will see two harnesses that connect to this sensor. Using a thin paperclip or pin, insert the paperclip or pin into the back of the GRAY harness (leave the harness connected) where the white lead is until it is fully seated. Start the car and get it warmed up fully. Use the positive lead on the voltmeter and attach it to the pin or paperclip that you inserted into the rear of the gray TPS harness. Ground the other voltmeter probe and get a voltage reading. You need to adjust the TPS to .46-.48 volts. To do this loosen the two mounting bolts that hold the TPS sensor to a point where you can rotate the TPS. Rotate the TPS until you get the correct voltage reading. Now tighten the TPS and recheck the voltage. If it remained good shut the car off, remove the pin or paperclip from the rear of the gray harness. Next disconnect the gray harness and start the car. Turn the headlights on and adjust the idle to the correct RPM using the idle adjustment screw that is located on the IACV unit that is mounted on the rear of the plenum on the drivers side. Using the screw adjust the idle to 800 +- 50 RPM. Once that is done let the car idle for about 30-60 seconds to make sure it is stable. After that reconnect the gray harness while the engine is running. Make sure the idle does not change. If not you are good to go.
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post #4 of 9 (permalink) Old 01-09-2009, 03:39 PM
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Re: How to adjust idle speed of a 90 Nissan 300ZX?

Alpha, why would the stock tach not be just fine? We're talking about setting idle speed, not doing ECU timing/fuel mapping, lol. I bet the stock tack is accurate to within 15-20 rpms, as if you would even discern that visually anyhow. MaxDoc rules as usual.
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post #5 of 9 (permalink) Old 01-09-2009, 04:40 PM
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Re: How to adjust idle speed of a 90 Nissan 300ZX?

I have seen many stock tachs which were off by more than 200 RPM. I never suggest people use the stock gauges for more than a general idea.

90 300ZX TT
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post #6 of 9 (permalink) Old 01-09-2009, 05:22 PM
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Re: Here is the best way....

MaxDoc Wrote:
-------------------------------------------------------
> After that reconnect the gray harness while the
> engine is running. Make sure the idle does not
> change. If not you are good to go.
> MaxDoc

If the idle does change, what component is the most likely culprit?

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post #7 of 9 (permalink) Old 01-09-2009, 05:30 PM
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I would look ...

at the TPS..
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post #8 of 9 (permalink) Old 01-09-2009, 05:42 PM
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Re: I would look ...

my boost controller registers what seems to be a reasonable percentage when actuating the throttle so that would seem to confirm that the TPS is working right?

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post #9 of 9 (permalink) Old 01-09-2009, 06:31 PM
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Not really....

the TPS also has a set of contact points that tell the ECU the throttle is off idle. If the contact points do not work there could be an issue with the idle among other engine control systems such as the fuel cut off. That is the harness that connects directly to the TPS "nose".
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