Idle fluctuating/bouncing Problem on start up/neutral

miatalife04 · Post by **miatalife04** » Sat Nov 12, 2016 6:25 pm

Hi everyone! its about time i associate with fellow mx5 citizens on forums! This is my first post ever!

Ok so nows the time i finally get off my backside and ask for some advice about my wee idling problem.

I own a JDM imported 1992 MX5 1.6
When i turn my car on start up, sometimes my RPM fluctuates on idle. The tachometer needle is bouncing up and down around every 1.5seconds going from 1.5K RPM to a very low 400RPM - to the point where the car shudders as if about to stall. It does this all by itself! The rpm fluctuating range does changes sometimes but generally it fluctuates between 2K RPM and 0RPM! When it does this it carries on for a good 15 odd seconds, sometimes only for 7 seconds.. then it finally goes back to normal idle speed at 850RPMs
I also noticed that even when i turn my car on it sometimes just revs at 1.5KRPM on idle! For a few 15 seconds then going back to normal RPM idle speed again..

I have tried pressing the clutch in on idle but it doesn't effect the fluctuating and have also tried revving up a bit to 'shake' the RPM needle, sometimes it goes back to normal rpm idle speed,
but sometimes it doesn't do any change until it makes itself go back to the normal RPM idle speed!

Also ill include when i slow down and stop at a stop light it will sometimes with a small chance do the fluctuating thing In neutral, but the needle only bounces at a smaller range (1.1K - 700RPM)

When i drive, it dosent seem to be any noticable weird things happening (except the lack of mx5 low end torque of course! haha)

I have tried to inspect air vacuum line leaks or cracks on the black intake pipe and the silver Air Flow Meter. There seems to be no problem.. unless i have missed something!

Can anyone please advice me and hep me isolate the problem so i can cure this zombie idle controlling itself problem!

Post by **jif** » Sat Nov 12, 2016 8:18 pm

Sounds like the idle air valve needs a clean and adjust!

miatalife04 · Post by **miatalife04** » Sat Nov 12, 2016 8:42 pm

Thanks ill have a look into inspecting and cleaning my IACV

also;

Edit: Oil pressure guage needle also fluctuates with the RPM

miatalife04 · Post by **miatalife04** » Fri Nov 18, 2016 3:51 pm

Ok so ive finally gotten around to setting my base idle point on my MX5, ( now the storm is away haha)
when i jumped TEN and GRD the revs only went up above 1K around 1.1K, ive adjusted the idle screw to match the 2 idle points on proper idle speed (around 850RPM) and there was no blinking on the dash for codes when jumped.

It hasnt eliminated the idle bounce.
and now.. i have noticed the rev bouncing on the idle used to be from 1.5K to like 400RPM - now from 1K to 300RPM

that damn fluctuate is still there! it just doesn't go as high

what should i check next?

~Mark

Teamjelly · Post by **Teamjelly** » Sun Nov 20, 2016 9:25 am

Unplug the idle control valve and see if that settles the idle
If it does you've found the cause of the problem - Dunk it in a container of Brakleen or Heavy duty degreaser for 24 hours and give it a good scrub and blowout.
If it doesn't make a difference - then it could be a lean hunt at idle
So check the fuel filter, Fuel pump, AFM and regulator - in that order
Pull the plugs out too and see if they are white indicating a lean mixture.
If none of that helps - then I have an LS-1 Motor here we could drop it - that will solve it

miatalife04 · Post by **miatalife04** » Wed Nov 23, 2016 5:45 pm

Do you know any good articles on how to clean/remove the IAC?

Teamjelly · Post by **Teamjelly** » Wed Nov 23, 2016 5:52 pm

Articles?????
Remove throttlebody - Remove IAC valve
Dunk in bucket of petrol and leave for 24 hours
Take wifes toothbrush and scrub the crap out of it
Blow it out with compressed air
Put wifes toothbrust back where you got it from

miatalife04 · Post by **miatalife04** » Sun Dec 11, 2016 10:28 pm

Greetings everyone, after a bit of MIA with work and all, I am now back to trouble shooting my mx5.
So, I have read the 'MX5 NA ISC Trouble shooting article,' from Miata Garage and i have decided to first start off with spraying some Carb and TB cleaner into one of the air tubes into the ISCV, According to this text in the article =

~(CLEANING: �A first non-invasive cleaning can be attempted by spraying throttle body cleaner (I used Berry B12 carb. & TB cleaner) into the air supply tube to the ISCV with the engine running.� It is possible to remove the front end of this tube near the throttle body and seal the black molded plastic intake air chamber port with a cork. (see picture)~

The reason i choose this method first is because i simply lack knowledge from removing my TB to remove the ISCV for a full clean up! Also i am scared i might break my car (lol!) So i think this is the best option for me because it is easy and simple for now!
I am popping over to the local parts store to pick up a $9 Carb and TB cleaner and will hopefully get this troubleshoot underway along with my full brake pad and left headlight bulb replacement!

just to also let you know at some rare scenarios my car now performs the idle fluctuate and actually drops to the point where my car stalls

it hasnt happened at a stop light yet, only when ive been parked, i just wait for a few seconds, and when i turn my car back on i blip the trottle a bit and it mysteriously goes away back to normal idle or will only drop to 'just before stalling'.

one more thing... I have noticed I have developed a 'rev hang' on my mx5 where I perform an upshift and when i fully depress my clutch with my foot already off the accelerator pedal, the RPMs seem to increase a tad bit before dropping down... does anyone know a thing or two about this?

Thank you all for giving me advice so far

~mark

Idle fluctuating/bouncing Problem on start up/neutral

Idle fluctuating/bouncing Problem on start up/neutral

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