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1. TPS

Am I thinking on the right track?

In an effort to try and narrow down my idle issues, (idling at between 1400 & 1800 rpm when hot), I have been trying to adjust my TPS as per the manual, as I did stuff around with it before I knew what I know now. So, with feeler gauges & multimeter, I had it perfect, tightened it up, rechecked it still good. So I went for a drive & came home & rechecked it only to discover it's out again. So I pulled the cover off to have a look.

I think it's worn. Inside is a cam type thingy that pushes the copper points together or lets them separate. It seems to have a bit of slop/free movement. I'm thinking this explains the loss of continuity, i.e it moves a tiny bit breaking the connection?
I've got a new TPS coming in the next few days anyway.



2. Next up, I checked the air valve to make sure the piston was moving as required (it was). But my question is: When the piston is in the "hot" position & therefore blocking the air passage, how tight is that seal? I'm thinking for it block air it would also be liquid-tight? But, with the piston in the hot position, I sprayed WD-40 into the spring side and it slowly leaked into the other chamber. Is this normal?

Sorry for the left field questions, but surely someone can enlighten me.

Cheers

1. For high idle these are also worth considering if you haven't already:
viewtopic.php?f=29&t=40022
viewtopic.php?f=29&t=55085

2. This should tell you if not already checked: http://www.miata.net/garage/isc.html

Thanks Clubman,

Ok, so now I'm at a loss. The new TPS made no difference. The weird thing is, I'll drive for a bit, stop, and it idles alright. Then turn it off and start it again straight away & the idle is high, but not always. Another point to note, is when I bridge the TEN & GND terminals there is no noticeable change in engine speed or sound, so I'm hoping it's not ECU or electrical, as I'm not overly electrically minded. I'm going to pick up a new rear temp sensor & I'll have a look at the clutch switch. Is there a way to test the clutch switch with a multi-meter?

What I've checked so far:

Air valve - seems ok
ISCV - cleaned
New TPS
TB - cleaned & resealed butterfly
No Vacuum leaks that I can find

There are also no fault codes showing up, but I reset the ECU anyway, and it made no difference.

Anyone got any other ideas?

Apart from Russellb, recall Manga Blue has posted about clutch switch, so it might be amongst these:
search.php?keywords=clutch+switch&terms=all&author=manga*&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Rod's Enthusiast Manual for the NA8 says after disconnecting battery: unplug clutch switch wire & connect a multimeter across the clutch switch terminals - continuity is shown when pedal is depressed, & no continuity should exit when pedal is released. If not as specified fit a new clutch switch.

Thanks clubman I'll hit that tomorrow.


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Well I only got time to basically have a look at the clutch switch. A few things I noticed were: the actuator doesn't stick out of the switch so I'm guessing a broken spring inside. Also the blue stopper is missing so the switch would not be actuated anyway, so I'm going to remove it today to investigate further.

I also did the click test on the ISCV - Fail. When I unplugged the connector the revs increased as they should, but didn't drop when reconnected.

I'm starting to think I could have multiple faults here.


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This morning I pulled the clutch switch out and it had a broken spring, so I pulled it apart and put the spring from a ballpoint pen in (perfect fit), tested it and it works. I also put a rubber stopper on where the blue one was supposed to be. This has not solved the problem. Next I fitted a dead end gasket between the air valve and the inlet manifold to rule out a faulty air valve. It's not the air valve.
So then I tested the ISCV with a multimeter, when I first touch the terminals, the meter briefly flashes up a reading of about 100 ohms then zero. So I'm thinking the ISCV is stuffed. I have not yet replaced the rear thermosensor.

Thoughts?

And you DEFINITELY have no air leaks?

Dann

Dann

I've sprayed water around all the vac lines, & I'll never say never, but to the best of my knowlege I have no vac leaks.

What did you hope to find with the water?

Typically you spray degreaser or instant start around all of the joins and the engine will suck it in and the revs will rise.

Dann

I was told water will do the same thing more safely.

There's a gearbox neutral switch as well. It's on the high left side of gearbox with leads over the top to connectors near the right side of gearbox. Idle will be high if it thinks it's in gear and clutch pedal is not depressed. You can try disconnecting the 2 leads at the connectors and seeing if shorting/opening across them does anything.

manga_blue wrote:There's a gearbox neutral switch as well. It's on the high left side of gearbox with leads over the top to connectors near the right side of gearbox. Idle will be high if it thinks it's in gear and clutch pedal is not depressed. You can try disconnecting the 2 leads at the connectors and seeing if shorting/opening across them does anything.

With a working clutch switch, if the clutch pedal is depressed, wouldn't that over rule the neutral switch? Just my logic, quite possibly wrong.

That's the theory, but theory rarely seems to apply properly with high idle problems.