Another Rough Idle

300ZX

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buckers13
Posts: 3
Joined: Thu Oct 25, 2012 2:21 am
Location: Christchurch

Another Rough Idle

Post by buckers13 » Wed Sep 17, 2014 5:35 pm

Hi guys,

Have been having a weird issue that is getting a bit annoying.

So few months ago started to develop a rough idle. This would only happen when warm at first, and would just kind of bounce (normally sits happy at 900, but was just dropping to 500 up and down.)

So I checked the MAF gave it a clean, took out the spark plugs, checked they all seemed fine. Still no go. Gave up for on it for a bit and booked a mechanic.

About 2 weeks laters, as I'm on the way to the mechanics, it's just driving perfect. Like zero issues. I thought I just got super lucky, but should have known. Another 2 weeks pass and the problem comes back. Took it to a mechanic today, and they didn't even know where the Idle control was until I pointed it out to them. They ran for codes, gave a 55 so no errors. They believe that it is the ecu is broken even though they could watch all the sensors reading and reacting to the cars idle. I personally think it's the Idle control valve.

So my question here is. Anyone in Christchurch that actually knows how to work on z32s? I'm not that talented when it comes to mechanics and I don't have the tools or the space. Should I just go to Nissan and get them to solve this for me?

Any help would be mega appreciated.

Cheers, Chris.

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ZILVER
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Location: Auckland

Post by ZILVER » Wed Sep 17, 2014 7:33 pm

Hey Chris,
It could be a number of things. But I doubt its the ECU given the story + codes are reading all clear/55.
Given that it drives perfect one day and not the next its my guess that its most likely an electrical sensor or simply carbon build up in the Idle Air Control Valve - IACV/sticking things.
If you want to try eliminate the IACV as a culprit then its an easy DIY job to take it off and clean it with WD-40. This should clean/alleviate any stickiness and fix or at least minimize the issue.
(Heres a write up on how to remove/replace one)
The next cheapest thing to try is the Coolant temp sensor - this should be a maintenance/replacement item if not done so already (Is you sensor top red or blue? A blue one is the current design/type and is screwed into the front coolant pipe / looks like this: https://conceptzperformance.com/Cart/de ... php?II=580).
A failing coolant sensor will causes stumbles and rough idle/erratic behavior.
Last edited by ZILVER on Thu Sep 18, 2014 4:06 pm, edited 2 times in total.

Greensheep
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Location: Auckland

Post by Greensheep » Wed Sep 17, 2014 8:39 pm

Hi Chris
Couple of questions
Is your car a Z32 NA or TT?
And does it make a difference to the idle if you have the air con on or off?
Cheers David
It's always a good day when you drive a Z

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Logan
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Location: Auckland, New Zealand

Post by Logan » Thu Sep 18, 2014 6:16 am

Given that diagnosis I would certainly not take it back to that mechanic whatever you do. Is the car driven regularly? I had a similar issue recently with a Toyota that I narrowed down to stale fuel. Also when you say you checked the sparkplugs did you visually inspect the tips or checked they all sparked? Could be a coil pack breaking down which is fairly common for these.

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kirihi
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Location: Christchurch

Post by kirihi » Thu Sep 18, 2014 8:06 am

Hi there. We had a lot of problems with the crank angle sensor on our Z32 NA when we had it, with similar symptoms to yours. Steve Welford (Steve Welford Automotive) in Sydenham was/is my fix-it man, and he's a great guy. If you do go to see him, tell him that Chris (with the black 350z) sent you.

Good luck.
Chris D
2007 (HR) Magnetic Black 350Z Enthusiast

buckers13
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Joined: Thu Oct 25, 2012 2:21 am
Location: Christchurch

Post by buckers13 » Thu Sep 18, 2014 2:44 pm

Hi guys,

Thanks for all the advice so far. I can't actually do any work on it at the moment until my weekend which is a bit annoying.
Yes it is driven everyday and has never given me any trouble for about 7 years now.
I checked the tips of the spark plugs and gap. Didn't bother seeing if they sparked because they all looked pretty good. I guess I should check they spark next time to.
No difference with air con on or off.
It used to be just when it was warm it would go funny, but now it can do it anytime cold or hot (engine temp).

It's a 96 NA.

Again thank you all for helping.

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ZILVER
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Location: Auckland

Post by ZILVER » Thu Sep 18, 2014 3:53 pm

Bad spark or a vac leak would prove to be a constant issue, unless there's a poor or loose electrical connection somewhere.
You'd drop a cylinder/engine rumble shake if a sparkplug or coil pack failed. (You can test/hear it simply by disconnecting the coilpack connector whilst engine is running.) So unlikely they'd be culprits for a random/fluctuating symptom.
But good luck, let us know what solves it.

Greensheep
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Location: Auckland

Post by Greensheep » Thu Sep 18, 2014 8:30 pm

If the aircon on or off makes no difference then you can probably rule out ECU
The ECU has to increase/decrease the idle for the extra load of the aircon compressor
I would start with idle air and CRC
The next I would look at the coil packs, some coil pack stems crack and the spark escapes through these cracks
To test wrap insulation tape around the stem, note if this works it's not a preminant fix just a way to diagnose.
Good luck
Vacuum leaks are harder to find but I do have so tricks you can use if you need
It's always a good day when you drive a Z

DKNWSZX
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Location: Northland

Post by DKNWSZX » Fri Sep 19, 2014 9:47 am

There are three physical components that are strictly for the idle control of the car.

•Auxiliary Air Controller (AAC)
•Fast Idle Control Device (FICD)
•Air Regulator

The AAC and FICD are both solenoids that help make up the Idle Air Control Valve (IACV). The IACV also contains an adjustment screw for setting the base idle. The AAC housing receives air from the pipe connecting to the driver's side accordion pipe, and/or from the balance tube, through the air regulator.
Auxiliary Air Controller
The AAC is the primary controller for maintaining idle speed. It is a simple ON/OFF solenoid, and the ECU controls it with a varying pulsewidth, similar to a fuel injector. The higher the pulsewidth, the longer the solenoid is open, allowing more air to enter and the idle to raise. When the pulsewidth is lower, it's open less, and less air enters, lowering the idle.

Fast Idle Control DeviceThe FICD is a secondary solenoid. When it opens, it allows a specified amount of additional air to enter. It's purpose is to raise the idle immediately when turning on the A/C compressor, or when the power steering pump is under heavy load (turning the steering wheel while idling, for example). The additional idle speed is to help the engine compensate for the added load of these accessories, rather than simply stalling out.

Air Regulator
The Air Regulator is a shutter valve which uses a bimetal spiral spring to open or close. When the spring is cold, the valve is fully open. When the car is turned on, voltage is applied to the bimetal, causing it to heat up. As it heats up, the valve gradually closes. The Air Regulator's purpose is to raise the idle speed when the engine is cold. I think that this could be your culprit.

Some advocate removing the Air Regulator and capping it's ports, as the ECU will automatically raise the idle speed while cold through the AAC, obfuscating the Air Regulator altogether.
Good things are worth waiting for, but great things happen at once.

buckers13
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Joined: Thu Oct 25, 2012 2:21 am
Location: Christchurch

Post by buckers13 » Fri Sep 19, 2014 3:27 pm

So it turned out to be the coolant temperature sensor. Gave it a good clean and fired her up and she ran just sweet for 5 minutes idling away. So heres hoping the problem has gone and will never return again!

Thanks for all the help and suggestions guys.

Cheers, Chris.

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Jibber
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Post by Jibber » Sun Sep 28, 2014 7:36 pm

Probably worth investing in a tube of dielectric grease at super cheap or similar and dosing it. That little puppy mist take a hammering from road spray etc, and the grease will help it stay clean and contact better

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