1993 Miata will not idle

My car stopped idling all of the sudden and I can’t figure it out. Other than the idle issue, it runs fine. The engine is basically stock except for a header, exhaust, intake, and light-weight under-drive pulley. I have used this configuration since 2009.

Here is what I have done:

- Checked the plugs. Looked fine.
- Tested back-up set of wires.
- Used soapy water to test all of the vacuum lines, but I only tested the ends, not the rest of the lines. Hmmm. I will have to revisit the lines.
- Cleaned throttle-body.
- Tested air-valve using freezer and hair dryer.
- Replaced the PCV valve and grommet.
- Tested TPS with OHM meter.
- Tested secondary coils with OHM meter.
- Tested primary coils with OHM meter, but I did not get the expected results. Seems odd that it would be the ignition if the car runs fine otherwise. I was going to pull the ignition off a friend’s car and try it. Anyone think this is the cause?
- I do not have a CEL, but the there are two codes stored in there – 3 and 15. I replaced my O2 sensor a year ago. Even when it was malfunctioning, the engine did not act like this.

Any other ideas?

Maybe if you lost 20 or 30 lbs...

There is a write up in the garage section on the pointy board which covers idling issues and is specific to the 1.6.

I have issues where my idle will not come down immediately after coming to a stop. My idle will drop down to 1300-1400 rpm and after 5-10 seconds drops down to normal.

This is the pointy board article of which he speaks... http://www.miata.net/garage/isc.html

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Originally Posted by tailchaser

This is the pointy board article of which he speaks... http://www.miata.net/garage/isc.html

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Thanks TC, its not easy for me to put links in while on the phone (or maybe I just dont know how to do it!).

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Originally Posted by tailchaser

This is the pointy board article of which he speaks... http://www.miata.net/garage/isc.html

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Thanks. I thought I already checked everything in this, but I will check again.

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Originally Posted by Avarice

Maybe if you lost 20 or 30 lbs...

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Winning's not a problem. Just idling. ;)

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Originally Posted by jrj512

Winning's not a problem. Just idling. ;)

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Really I thought you got Hiromoto'd yesterday?? ::Rimshot:

IAC Tests out OK??

Unplug the IAC and see what changes. My money is on the IAC.

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Originally Posted by mr brg

Unplug the IAC and see what changes. My money is on the IAC.

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I think thats my problem too.

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Originally Posted by POS Racing

IAC Tests out OK??

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Originally Posted by mr brg

Unplug the IAC and see what changes. My money is on the IAC.

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Originally Posted by motorollow

I think thats my problem too.

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I think I mistakenly bundled this when I tested my TPS, so I never tested it. I will have to try it. Thanks!

"stopped idling" - Does it die when you take your foot off the gas or run at above 750 RPM?

Does it change with Ground/Ten connected on the diagnostics port? If so, what does it do?

Is the idle control screw still there? Did it shake loose?
On my '94, some one had adjusted the idle via the stop screw on the throttle cable instead of the idle control screw at the top of the throttle body. After adjusting the stop screw it would die until the idle control screw was adjusted.

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Originally Posted by EricJ

"stopped idling" - Does it die when you take your foot off the gas or run at above 750 RPM?

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It does down to a very low engine speed and then dies.

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Originally Posted by EricJ

Does it change with Ground/Ten connected on the diagnostics port? If so, what does it do?

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It does not improve.

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Originally Posted by EricJ

Is the idle control screw still there? Did it shake loose?

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Still there. I have not touched it, yet.

As usual, I bet you have something stuffed in your exhaust hole.

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Originally Posted by jrj512

Whining is not a problem. Just idling. ;)

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Fixed!

I don't know much about the other tests mentioned, but I would definitely take a good look at the rest of the vacum hoses. Also, how are your grounding straps/battery terminals?

Let me know if you are going to work on it any evening this week; I'll be happy to come by and keep Leilane company. (or help you, I guess...)

Does your car have the Racing Beat Sway Bar Brace Kit Hardware on it?

Not that that would have any bearing on your current problem but for some reason it just seems like a required question in the Miata Tech Section these days! ;-)


Did you fix it yet BTW??

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Originally Posted by POS Racing

Did you fix it yet BTW??

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I will not be able to work on it again until Wednesday or Thursday.

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Originally Posted by POS Racing

Does your car have the Racing Beat Sway Bar Brace Kit Hardware on it?

Not that that would have any bearing on your current problem but for some reason it just seems like a required question in the Miata Tech Section these days! ;-)

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http://4.bp.blogspot.com/_IF6Q-pCDIY...1g/shaddap.jpg

[QUOTE=POS Racing;270853]Does your car have the Racing Beat Sway Bar Brace Kit Hardware on it?

Not that that would have any bearing on your current problem but for some reason it just seems like a required question in the Miata Tech Section these days! ;-)QUOTE]

There is an easy explanation/connection to this idle problem with the sway bar brace. It is the magnetic resonance, the lacking of, which diminished the force field and makes your coil pack not working and hence the idle problem! Easy! :-)

If nothing changes with ground/ten connected, then it's probably not the idle air control valve. IIRC the ECU controls it. That's why when adjusting the idle screw ground/ten is connected.

If opening the throttle, just a little, fixes the problem, could something be clogging the idle air bypass?
On my '99, I had to do the intake manifold clean for the EGR valve issue. When I did it, I also pulled off the throttle body and idle air control valve and cleaned it with throttle body cleaner. The throttle then closed properly, causing it to die at idle and requiring re-adjustment of the idle screw.
I just squirted throttle body cleaner in the idle air bypass. I read not to remove the idle screw completely. It's hard to get back in.