Idle Speed Control Valves and safe failure modes

Finally. It has taken me a great deal of wrenching, cursing, and no small amount of money, but my 1992 Miata is finally running the way the good Lord intended, as she rolled off the factory floor in Hiroshima so long ago, the same year I started high-school in rural Connecticut. Back then I had no idea that this car would eventually be waiting for me, more than three thousand miles away and two continents later.

Well... of course, that first statement should come with a caveat or two. My example could do with a new soft top, a new timing belt and accessory belts, really, new rubber all around.

That said, it finally runs right. Yes, I'd say my example had some deferred maintenance. So far I've replaced:

• Shock absorbers (Koni Sports)
• Thermostat (was frozen shut)
• ISCV (failed, probably due to overheating when thermostat was stuck shut)
• Plug wires
• Air filter element
• Clutch slave cylinder
• Brake pads and fluid
• Battery (Duralast 8AMU1R)

Is that really it? It feels like I've done so much more. Maybe the fact that I've flushed the coolant three times while I was fighting the overheating issue, the fact that I've changed the oil and transmission fluid, spent so much time dealing with the sneaky idle control problem... I feel like I have more into the car than just a simple dollar amount.

The shocks are a good example. Far from being drop-in replacements, the Konis have a 12mm shaft that includes an internal adjustment rod - which of course won't fit through the factory shock mounts. So, I had to drill them out... under my carport, without the benefit of a drill press or even a bench vise. I have to admit that it's high time I set up a proper machine shop.

My latest adventure: replacing the idle speed control valve.



The old ISCV is on the right, with air intake tubing attached, and the new ISCV is already mounted on the throttle body. In the Miata (and I assume other Mazda cars from that era) the idle speed control valve can open to allow a calibrated amount of air past the throttle plate at idle to compensate for load. The best example would be the air conditioning compressor. Of course, as good engineers would, Mazda's realized that it would be safer for this valve to fail open. Far better to have the car able to run the A/C at a light if the solenoid actuating the valve fails. The alternative? The engine would either stall or do horrible things to itself at 200 rpm. So, the ISCV fails open, and your car idles at an annoying 1800 rpm. Yeah, that's how much extra throttle you need from a 1.6 engine to run a tiny air conditioning compressor.

Well... mine failed. Since my original ISCV would stop working as the engine reached operation temperature (later ceasing to work at all, cold or hot) my best guess is that the overheating problem I inherited with the car resulted in an broken conductor within the solenoid housing. If I can muster up the motivation, I'll grind open the housing and see if my suspicions are correct.

Either way, the 'new' one works perfectly. My baby now idles quietly and without fuss right around 800 rpm. It's beautiful. Even the valve assembly itself looks newer, which is strange as it was pulled from a '91. Either it was a replacement piece itself - possible - or that particular NA was parted out early on in its life. The $50 in cash from my local specialist was a lot less painful than the $500 new replacements fetch online.

So... my baby is now back to some kind of baseline. Handling and engine performance are 'stock-like'. This winter, it'll be ready for some proper modifications. I haven't decided exactly what I'm doing, but a manual steering rack is definitely going on, and the power steering hardware coming off. The steering is precise, but much too light.

One thing: if you take off the ISCV for inspection or cleaning, you probably won't be able to re-use the gasket that seats into the throttle body. At least, I couldn't. The gasket seated (I think) and promptly disintegrated.


I'll note that the gasket had swelled badly from being cooked for several hundred miles, and the rubber must have been pretty badly deteriorated. Since I was unable to source a replacement gasket, this time I went with a rubber/cork one that I cut by hand. I was considering a silicone sealant, but I'm weird and I'll probably want to pull the throttle body for inspection, at which point it'll come apart without a mess.

In retrospect, I should never have pulled the old ISCV for cleaning. It didn't do any good, and the gasket failure wasn't the best thing in the world to happen to my engine. Those missing pieces of gasket were nowhere to be found, which meant they probably went through the engine. That's not as big a deal as the rust on my old ISCV, which makes me think that small amounts of coolant were leaking into the intake.

Not good. So: don't do what I did and attempt to re-use that gasket. It wasn't broken for very long, though, and I think my car is ready to forgive me.

Do you REALLY need an airbag?

Actually, I just wanted to post this here so I could find it again.

Driver wearing 5 point harness walks away (laughing) from a 55 mph head-on in a Miata. Racing steering wheel installed.

It's kinda funny to watch the passenger bag blow. Heh.

Edit: NOT wearing a helmet.

Throttle Body and IAC (ISCV) Cleaning

Yes, that really is my car with the throttle body out and lying on the ground. I have no idea why there's a pile of rusting bike parts littering my work area, I need to clean up. Box that shit up. Yeah.

For the record, although you do see the Haynes manual pictured, it was pretty useless. This article is vastly more useful. Remember, of course, this is for the 1.6 - I don't know if the 1.8 is different.

I attempted a non-invasive cleaning with no real results. Apparently, so had the previous owner, as the main mounting screw for the plastic air intake had been removed. Permanently. So I need another one. However, spraying the face of the throttle restrictor plate is not going to fix idle problems.

When cold, my ISCV (idle speed control valve) worked perfectly, compensating for extra load (like A/C) exactly as it should. Idle was right around 900 with the idle control screw pegged shut. As the engine warmed, the idle would rise to about 1200-1300 and the ISCV would stop working completely. Turning on the A/C would almost stall the car at idle.

This made me think I had a very dirty ISCV. I mean, had it even been cleaned in the 102k miles the car had been driven? I have absolutely no records for this car.


Well, how does it look to you? I think it looks pretty filthy. That's the back of the throttle, by the way, with ISCV still attached.

The Haynes manual refers to the ISCV as the IAV (Idle Air Valve). I think that ISCV makes more sense, as there is another valve that's also an 'air valve' but responds to coolant temperature, not the ECU. I haven't been able to find that valve referenced in my Haynes manual.



ISCV removed. I think the hardest part of all this was putting that stupid gasket back in. It was way distorted, probably from heat, and much too big. Ended up using a simple, latex based adhesive on the back side of the gasket, applying pressure, and praying. I'm pretty sure it got back in it's groove, finally, as it's a very thick gasket and the ISCV seated without a gap of any kind and not a great deal of effort. But that was awful, and if you can find a new gasket for this, do so and save yourself some serious frustration. Or share with me your secret for getting a swollen gasket to stay in place.


Look any better? That's about halfway through cleaning it... I eventually pulled the gasket from the groove which proved to be a silly thing to do. Silly me.


Oh yeah, and that's the inside of my intake manifold looked before cleaning. Nice.

That's about all there is to it, really. I'm happy it all went back together, the ECU isn't throwing open ISCV solenoid codes like it used to sometimes, and so far it seems the idle problems are cured. At least, the ISCV problems. I now get a nice steady idle at all engine temperatures and the ISCV works whenever I test it. Of course, it's not over - I am suspicious of the other air valve. But that one's a lot easier to get to.

Serious Surgery

If that looks like my workstation laid out on my couch and getting it's guts torn out, it's because it is.

I have suffered a most impressive list of hardware failures over the past week or so. First my notebook hard drive simply failed without warning (sounds like the head motor is toast, as it spins up but no seeking sounds and won't be recognized by any BIOS). Boo.

So I start using my desktop for primary use. I buy a monitor to make it usable (a 37 inch LCD TV is fun for about 5 minutes) and the power supply, coincidentally, decides to give up the ghost after 5 or 6 years of faithful, continuous service.

I guess that's part of my problem. Notebook hard drives aren't really designed to be left on for two years. I should never have been using a notebook as a primary workstation. Even my ancient desktop suddenly made me realize how bad the memory and disk I/O bottlenecks are in a laptop.

Oh and then the hard drives fail in the workstation, one after the other. I guess five years of continuous use is reasonable for a consumer hard drive... and they did travel 2500 miles across the country not that long ago.

But then I bricked my motherboard. That was really dumb of me. The old BIOS images ASUS supplies for its legacy boards are apparently incompatible with their newer Windoze based flashing software. So let that be a lesson to you!

Let that be a lesson to me, actually.

For about $130 I upgraded to another crap motherboard and bottom of the line processor, and it's just orgasmically fast. No, really. So, I think the only thing that's still left in my workstation is the DVD writer - everything else has been replaced in the past couple of days.

Hardware fails. Back your shit up. That's the lesson for last week.

I Hate VB (Don't You?)

I have no idea when I wrote this, but I was digging around in an older module, and found this ode to the most busted language ever written (apologies to COBOL):

' i hate vb
' -------------------
' a poem by henry j. mason
'
' i hate vb
' quite passionately
' i hate vb
' and it's clear to me
' that while there will be more to write
' (and write until my hair turns white)
' my love for programming has waned
' languished under basic's bane
' indeed, so fundamentally broken a language
' could do naught but cause in the most boring programmer deep, bitter anguish
' a twinge of pain
' as again, and again
' the sisyphus must recite
' the banal syntax, and despite
' obsolescence, this poor slave knows there will never be
' true death for such mediocrity
' unkillable, the vb zombie
' feeds, slowly, feeds... upon you, and me

Clearly I am somewhat passionate about this subject. The same could be said, I suppose, about any legacy language left in place to support some vital business function, and maintained in perpetuity...

VB (and don't talk to me about VB.Net, as that's a whole 'nother can of worms) irks me mostly as it was created to allow non-programmers to write code. WHAT?? Non-programmers should be kept as far away from a compiler as possible.

It's funny, though. Microsoft has long had a reputation as being user-unfriendly, beyond surface details, at least. It requires a very competent user to keep a Windows system running smoothly, even more so in the age of the Internet. It's a hackers OS, to a point, and that's why I like it.

Maybe that's why, when they try and make something for the non-hacker crowd, they fail so epically?

Experiments in Raw Feeding

So, we get home from a week in the gorgeous city of Cleveland, only to find this note from the dog-sitters.

My first reaction was disappointment. Man! I missed my baby's first kill! What a bummer. I also felt bad for the rabbit. Visions of it suffering on my back lawn as the dog sitter held back the slavering woof-woof went through my head. Oh well. It could have been hit by a car.

Then, inevitably, I started wondering what happened to the rabbit. Had they buried it? Thrown it in the trash? Apparently Miyuki had caught and slain her prey only hours before we got home. Good timing, as it turned out. A message to the dog sitter confirmed the presence of a freshly killed cottontail in a bag in the garbage container under the car-port. It was a cool, 55F day. I wasn't worried about spoilage. So, out of the trash came one big-ass bunny. I'm guessing it was over three pounds, as fully dressed it came to 2.25 pounds on the scale.



Yes, I cleaned and 'dressed' it. That is, whacked it into half pound sections with a cleaver. I'm pretty sure my neighbors think I'm certifiable. I regularly hack up carcasses on the patio. Is this normal?



I've never cleaned and dressed a mammal before. Gutted plenty of fish. I have to admit, as a vegetarian, it really wasn't that bad. I mean, I don't plan on eating it - it's going to those that deserve it, our dogs.




The fact is, rabbit meat is expensive. Ground or whole expect to pay $7 a pound. There is, as far as I know, little demand for it as food for humans, it's the raw feeding movement that make this meat so lucrative.

So, all is well, and whatever guilt I felt about the suffering of the rabbit has been assuaged. It's painful end shall not have been in vain - it will be consumed, and the life cycle shall continue.

It's now in the freezer for a month. We'll see how they like it.

Trouble...

There's something new in my driveway. Something that's just begging to be tinkered with.