Intermittent high idle problem- need diagnosis help!

[bensale]

Thanks Jeff, i have the haynes one and the mazda one as a pdf (thanks rotary ) I would be interested in checking out the Enthusiasts guide. I should have been in Sydney this weekend for work but that fell through so I'll be there on Sunday

Now, with the current throttle body on the car is idling acceptably. However it is still wrong...

I have screwed down the idle adjustment screw in the throttle body as far down as it will go. Doing this should mean the car will stall... However with the ten and gnd terminals joined the manual idle speed is around 1000rpm... The computer controlled idle is around 800-850rpm. At the moment it is acceptable as the car doesn't idle too high anymore. Most of the time when coming to a stop the car will idle at 1000 rpm for a few seconds before settling down.

This makes me think that I must have an air leak somewhere around the throttle body as through screwing the idle speed adjuster down all the way it should be blocking off all air to the intake manifold. If functioning correctly this should mean the car won't run without the throttle valve open... SO I think there must be a leak somewhere...

So I'm thinking of taking the thottle body I have on now off.
Give it and all the surfaces it mates too a good clean.
I put a new gasket on when I changed over to the current throttle body so that should be fine.
I will also adjust the throttle body valve so it is set correctly, setting the stop just on the point where it cracks open.
I am pretty sure the problem is not before the throtle body judging by the fact it still idles so I shouldn't have any problems with any air supply hoses.

Hopefully that can give me some form of resolution.

What do we think?

[Juffa]

Hi Ben,

I was just digging around for something else and I came across some information that might be of some assistance.

As mentioned previously there is a clutch switch and a gear box switch. I had forgotten about the throttle position sensor. It is a combination of these three that control the revs at idle.
When the car is in neutral or when the car is in any gear and the clutch is depressed, and the TPS senses that the throttle is closed the engine revs should be around 850 Rpm. If the TPS, or gear box switch or clutch switch are faulty the PCM will not control the engine revs correctly.

Or buy my ecu so we can see if one of the switches or the TPS is at fault.

J

[cshaks]

Hi Ben, here is an answer that is kinda out of left field.
How old is your battery, and what kind of volts is it cranking out at start up?
The reason that I ask this is that some systems use a known voltage at start up to find and control what is known as a home position.
Some years ago I had a 323 astina that I was told by mazda had dodgy idle stepper motor, (big money item...!) had issues with idling, hunting and all that kind of stuff. I replaced the battery and the problem disappeared immediately.
It may be worthwhile just checking your battery against a known good one???
As I said it's a long shot, but it may be worth it just to try???

Cheers
Chris

[bensale]

Thanks Jeff, although from the sounds of it I'm a bit late for your ecu The TPS deserves further consideration though, I'll look into it.

Hi Chris, thanks for that. I'll hook a multimeter up to it and check that out. While it still works fine the battery is fairly old and has been killed and brought back to life with a triccle charger a few times.

[Juffa]

Thanks Jeff, although from the sounds of it I'm a bit late for your ecu The TPS deserves further consideration though, I'll look into it.

Hi Chris, thanks for that. I'll hook a multimeter up to it and check that out. While it still works fine the battery is fairly old and has been killed and brought back to life with a triccle charger a few times.

Tweety is up on stands at the moment while I prepare to remove the LSD. You are welcome to borrow my OEM AGM battery to see if that helps.

J

[cshaks]

Thanks Jeff, although from the sounds of it I'm a bit late for your ecu The TPS deserves further consideration though, I'll look into it.

Hi Chris, thanks for that. I'll hook a multimeter up to it and check that out. While it still works fine the battery is fairly old and has been killed and brought back to life with a triccle charger a few times.

No worries at all mate.
Like I said, its a little out of left field as far as a solution goes, but it may just be worth a try.
Let me know how you go!

Cheers
Chris

[manga_blue]

Ben, I still think you might be describing a simple TPS adjustment problem. Remove the TPS plug, loosen the TPS mounting screws, connect a multimeter across the 2 bottom pins, turn the TPS so that the multimeter reads closed circuit (0 ohms) when closed and changes to open circuit when the gap between the throttle stop screw and the tab on the throttle body approaches 0.7mm.

Or, as per Mazda ...

TPS1.jpg

TPS2.jpg

TPS3.jpg

[bensale]

Ben, I still think you might be describing a simple TPS adjustment problem. Remove the TPS plug, loosen the TPS mounting screws, connect a multimeter across the 2 bottom pins, turn the TPS so that the multimeter reads closed circuit (0 ohms) when closed and changes to open circuit when the gap between the throttle stop screw and the tab on the throttle body approaches 0.7mm.

I'll try that tomorrow!

Thankyou for the brilliant instructions

I still haven't tested the battery, I'll do that tomorrow as well.

Cheers,
Ben

[bensale]

Guy, the TPS is functioning perfectly... Closed it reads 0 ohms and then reads open as it should... Would have been nice if that was the problem.

When starting the car the battery outputs aprox 9v for around half a second (while the starter motor is engaged) before outputing aprox 14v there after... What is the consensus on that?