mx5cartalk.com

Hey Guys,

Malibu's cranky with me.
The idle has shot up to 1500rpm for no apparent reason. The funny thing is that when the a/c kicks in the idle drops down to 1000rpm (which is where it should kick UP to from 800-850rpm). I know this for a fact because when I turn off the a/c completely the idle goes back up to 1500rpm.

I've bridged GND and pin 10 on the diagnostic connector, and wound the idle screw in all the way, and got the sucker to 1000rpm, but that's still way too high. I would have thought I should be able to stall the engine screwing it all the way in?

Any ideas?

Thanks
Jules

We've been having idle issues aswell... ive been reading somewhere round here about the idle control valve and that you can try giving it a bit of a clean.

Vacuum leak somewhere?

Hey Jules. does it only happen when the clutch pedal is depressed?

Tweety did this and I found that there is a small white switch attached to the clutch pedal. A circuit closes when the pedal is depressed. In my case the spring inside the swithc had broken and circuit did not close. I ended up going to Jaycar electronics and buying a cheap swtich and taking the spring out of it and putting it in the mazda switch...all fixed.

J

I tend to notice it when I stop in neutral in traffic. So, clutch engaged?
I don't think the clutch in or out makes too much difference, but I will have a check this afternoon.

Jules

Check the hose going onto the IAC valve (underneath the plenum) is securely sealed.

The control valve, or thermo valve, on the 1.6 is on top of the plenum. I have taken this off and done a check with boiling water (much like a thermostat) and it works fine. It's closing nicely at boiling point
I am thinking that perhaps the ISC (idle speed controller), under the throttle body is not closing properly at warm up, allowing intake air to flow up behind the throttle body assembly bypass hose into the plenum?
I think this because if I disconnect the hose that feeds from the plenum side of the intake to behind the throttle body, and block both ends, the idle improves significantly. This tells me that perhaps there is intake air getting through the ISC, which would cause the same result as the throttle butterfly opening.

Does this sound feasible to you guys? I hear that the ISC is really expensive...

Jules

That's exactly what it sounds like to me.

Adjusting the minimum throttle stop with the screw only changes the minimum opening size of the intake butterfly - so I figured that air is getting around that - ie via the idle air control valve/idle speed control/whatever you want to call it.

Yours is either stuck, sticking, or leaking.

Mine is doing the same thing, an NA8. I had it serviced 4 days ago too, both the 140,000 and 150,000km combined, it had been doing it very occasionally, and a day after service it is now sitting at about 1800rpm at idle all the time. Taking it back Monday. This was Mazda, and all they said needed doing was 2 new tires.

As I mentioned previously, am having the same problem. It is doing it all the time now, but I drove in a spirited manner before, nearly redlining a bit, and then sitting at idle, no problem at all. Strange, it shouldn't make any difference, maybe it was just one of those moments it decided not to play up?

Well, as an update. The ISC from Mazda was $471 + GST

One call to Richard at MX-5 Plus, and a two day wait for the mail and I have not only an ISC, but a complete throttle body with ISC attached for $55.00 DELIVERED!

Bloody awesome service. I'll fit it on the weekend and let you know how I go. Fingers crossed.


Jules

Richard's a champ. Let us know how it goes.

Richard is a bloody legend!!!!!!!

Good to hear all is still on track.

On track? Yes, oh yes it certainly is.

Jules

Keep us informed of how it goes, I had my car back to Mazda and wouldn't you know, it was fine for the 3 days surrounding the check, they found nothing wrong, and the very next day it is doing it again...