New bug, fast idle.

For what it's worth:

Similar symptoms in my '92; turned out to be a faulty/shot "thermistor." (The thing is located near the firewall, I think on the block.) It sensed the engine water temperature to be cold, when in fact it was normal running temp. The ECU, thinking "cold engine," upped the idle to

1800 rpm, just as yours.

Although I don't remember, the part was quite a bit more than $1.98.

Let us know what you find out.

'92 B; red, of course

Stuff wrote in news: snipped-for-privacy@stny.rr.com:

Darn, I was afraid of that! I don't think that would cause an intermittent failure though?

I will, I'll probably have to take it in and sell a couple of the children to pay the bill....

XS11E,

I have a few suggestions...they may not be right, but they're free/very cheap to check.

1) Check to make sure the cable pulley is well lubricated along both the point-of-contact with the cable and where it connects to the throttle body. On the cable I'd recommend lithium grease, but others might say otherwise for the actual joint.

2) Remove the intake piping from the throttle body. Say hello to your butterfly valve. With your (clean) finger, poke at it (on the bottom half, I believe) and see how easily it moves. Keep an eye out for any obstructing debris in there. Lubricate where the butterfly valve joins to the throttle body.

3) This may be a case of a loose idle valve somewhere. Notice how when the car is cold, it idles at a different speed? There's usually two idling lines that allow specified amounts of air in. I'm not sure how this works on a Miata, but it's something to look into.

4) Gas pedal sticking?

Also, some things to ponder: does it only happen when it's that absurdly hot out? Does the idle jump even higher when you turn on the AC/radio/12V microwave oven?

Keep fiddling!

-r0ll

Thanks, I appreciate them!

I'll check that. Hadn't thought of doing that.

I don't think it could be anything in there causing the butterfly to stick because I've tried closing it from the outside and it seems to be closed tightly but I'll take a look and see what I can find from the inside.

No, the cable is slack when the car is idling fast so I've eliminated that, along with the cruise control cable, etc. The problem has to be right at the throttle body but from checking so far I'm pretty sure it's the ECU telling it to idle fast, not the butterfly failing to close.

I don't know, we've only got a cool nice comfortable 110F and won't get down to the too-cold-to-support-human-life temperatures of 85F and below for several more months...

Here's something a bit weird. Before the problem, when I'd turn on the AC the idle would start to drop and almost immediately go back to a normal 1,000 rpm. Now, when it's idling up at 1,800 turning on the AC acts the same, the idle speed just barely starts drop and then immediately goes back to 1,800. It's as if the ECU is saying the correct idle speed is 1,800rpm and is keeping it at that speed AND that's why I don't suspect any mechanical problem but... I'll keep checking as that's all I can do.

Oh, FWIW, I've not had a "check engine" light at all, whatever's happening the computer thinks is normal.

snipped-for-privacy@yahoo.com wrote in news: snipped-for-privacy@g10g2000cwb.googlegroups.com:

OK, the fast idle problem is fixed. Anyone want to make a guess as to the problem? The first one to post with the correct solution to the problem will win a one year free subscription to Nigerian scam emails!

The wire fell off the temperature sensor.

Lanny Chambers wrote in news: snipped-for-privacy@newsclstr02.news.prodigy.com:

Not even close!

Um...the tach was wrong, and it wasn't actually idling too fast?

Crikey, how should we know? :-)

Lanny Chambers wrote in news: snipped-for-privacy@newsclstr02.news.prodigy.com:

I wish one of you had told me, apparently it's not a rare problem. I took it to Mike's Place:

After talking to Mike on the phone, he just asked the year and then said it might be the IAC but most likely was the PVC valve and he could look at it at 2pm.

The PVC valve had lost it's innards and was just an empty shell. The extra air caused the ECU to add fuel and the car ran just like I was stepping on the gas. Since the problem was entirely mechanical, no Check Engine Light.

Mike had a PCV valve for $5.00 and I was off and running (with proper idle speed) about 20 minutes after I brought the car in....

As I've said hundreds of times before, it's hard to diagnose a problem as fast as someone who's seen it before!

"XS11E" wrote

Polyvinyl Chloride valve? Sorry, I couldn't resist. This is the first time I've heard of the PCV valve on a Miata going bad. Not that they can't, or I know all about Miatas, but.....

Information tucked away for future use. Thanks.

"Ken Lyons" wrote in news:E7ohg.9482$3i3.6052@trnddc08:

Mike indicated this wasn't a rare problem although I didn't see anything on Miata.net about it?

It was empty, just the outer shell, the innards got sucked/blown/whoknows? out completely. I was concerned as to the whereabouts of the innards but he said they got trapped Iforgotwhere and couldn't do any damage.... I suspect the valve itself is a plastic disk or ball like most of them so there's probably nothing to worry about, it'll just fall down and block all oil flow to the main bearings or something similar given my typical luck.

YOu bought new shoes in wide and now you are heel-and -toeing at stop lights

M. Cantera wrote in news: snipped-for-privacy@4ax.com:

Bad guess, it idles fast even if I drag my EEE shoes out of the car. The problem was the PCV valve.

Ah. Should have known. I actually have heard of it "going bad" on the Miata.net forums, though no one ever mentioned *how* it went bad. Glad you figured it out, you might have been on a wild goose chase for some time eliminating possibilities...I'll tuck this into my head as well...

Cheers,

-r0ll

XS11E wrote:

"r0lliSl1fe" wrote in news: snipped-for-privacy@u72g2000cwu.googlegroups.com:

I wish I could say I figured it out, took it to Mike's Place:

and he gave me the impression it was a fairly common problem. Anyway, it's fixed and I'm happy but poorer...