Weird high idle problem?

phaedo · Postby **phaedo** » Fri Mar 23, 2007 1:14 am

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...

jules · Postby **jules** » Mon Mar 26, 2007 1:45 pm

OK, an update.
New Idle Speed Controller is in and the problem is SOLVED!
Malibu's idling like a baby snoozing again when warm.
The old ISC came off and was found to have absolutely no resistance between the terminals. It had basically gone open circuit.

The job of removing the throttle body and ISC is s snack. The gaskets though *&^%^%^ I would have spent an hour just cleaning the throttle body to plenum mating surfaces. Total PITA.

Anyway, for those who's idles have risen to unacceptable levels, have a look at the ISC, or the Intake Thermo Valve, which is one piece on post '93 cars, but separate on earlier models. One of these bits of kit will probably be the issue.

Big thanks go to Richard at MX-5 plus for the brilliant and speedy service.

Jules

Babalouie · Postby **Babalouie** » Mon Apr 23, 2007 2:55 pm

jules wrote:OK, an update.
New Idle Speed Controller is in and the problem is SOLVED!
Malibu's idling like a baby snoozing again when warm.
The old ISC came off and was found to have absolutely no resistance between the terminals. It had basically gone open circuit.

The job of removing the throttle body and ISC is s snack. The gaskets though *&^%^%^ I would have spent an hour just cleaning the throttle body to plenum mating surfaces. Total PITA.

Anyway, for those who's idles have risen to unacceptable levels, have a look at the ISC, or the Intake Thermo Valve, which is one piece on post '93 cars, but separate on earlier models. One of these bits of kit will probably be the issue.

Big thanks go to Richard at MX-5 plus for the brilliant and speedy service.

Jules

Aaargh, mine's started doing it today. 1500rpm idle for long periods and sometimes it'll slowly creep down to normal, but at the next traffic light it's 1500 again.

So this ISC gizmo is below the TB you say?

jules · Postby **jules** » Mon Apr 23, 2007 3:50 pm

Yep Babs. That's right. Under the throttle body with a few hoses attached and a plug.

Your's will have the thermo unit attached as one piece (post 93). I would not recommend buying a new unit due to the ridiculous cost.

When they go or get stuck, they let additional airflow into the plenum causing the 1500rpm idle. It can be intermittent or, as in my case, happen after initial warm-up.

Let us know how you go. I think we're going to start seeing a lot of these with the ages of most NA's out there.

Jules

Astroboysoup · Postby **Astroboysoup** » Mon Apr 23, 2007 4:04 pm

nice work!

had a the same problem on my friends NA6.. we just cleaned it with carbie cleaner and it worked again.

Babalouie · Postby **Babalouie** » Mon Apr 23, 2007 5:42 pm

Hmm...Ok, I'll try removing it and dousing it with copious amounts of carby cleaner and then we'll see what we can see...maybe we can disconnect it or bypass it altogether?

jules · Postby **jules** » Mon Apr 23, 2007 5:47 pm

You should be able to bypass it by blocking the intake to ICS hose. Not sure how it will affect the idle at cold though.

Have a look at the intake pipe that runs across the front of the engine near the throttle body, and you should see the small-ish hose that runs to it. Block that and the problem will go away when hot.

Jules

bensale · Postby **bensale** » Sat Nov 07, 2009 3:07 pm

Thanks for this thread, been having the same problem over the last week... Know how to fix it now :wink:

Thought i would bump the thread up as it wouldn't surprise me if i'm not the only person having this problem.

Just a fit of advice, don't try and adjust down the manual idle speed to standard when the car is idling at 1500rpm, as when you go for a drive next time after it has cooled down it won't idle and will stall :wink:

manga_blue · Postby **manga_blue** » Sat Nov 07, 2009 11:10 pm

There are 3 other things that help set idle speed: the gearbox neutral switch on the top of the gearbox, the clutch in switch on the top of the clutch pedal and the throttle closed switch on the throttle body. If any of these go then you can get high idle speeds as well.

Just check:
1. High idle when in neutral and with clutch in = Throttle sensor switch faulty or out of adjustment
2. High idle when in neutral with clutch out = stuffed or disconnected neutral switch
3. High idle when stationary with clutch in = stuffed or disconected clutch switch

Throttle switch is adjusted so it changes from closed to open circuit across bottom 2 pins when gap between throttle plate adjuster screw and throttle plate stop approaches 0.7mm.

bensale · Postby **bensale** » Mon Nov 16, 2009 12:44 pm

Thanks for that phil. It idles at 1500 rpm irrespective of the three things you told me to check. So i can cross them off the list.

The problem is intermittent. i tried to make it occur on Saturday so i could check it out, of course it wouldn't do it, the car ran perfectly...

Today when the car was idling high i squeezed the smallish hose Jules mentioned running to the throttle body, blocking it off. The idle instantly dropped.

So I guess it is the Idle speed controller. Dropped by mazda on my way into work. They want $580 for a new one :shock:

So on the lookout for a second hand one. Off to the mx5 centre on Saturday i guess...