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Billy_Bottle_Caps SuperDork
10/24/19 9:36 a.m.

Great story cool car and great concept. 

Keith Tanner
Keith Tanner MegaDork
10/31/19 8:33 a.m.

With other projects out of the way, it's time to do a bit of work on 338. The biggest problem is that high idle. I'd tried troubleshooting a couple of times when I was visiting Mom and Dad but never seriously. A bit more prodding around had me thinking it was the idle air valve, which can get sticky with time. But to pull it off, I have to crack into the cooling system and the car's due for a timing belt.

So now it's timing belt time!

First, let's get on the lift. It's easy to forget how much droop travel these things have from the factory.

Underneath, it looks pretty clean. While it has seen some winter driving in the early days, it hasn't seen any since 1999. Also, check that smooth case diff - that's a mark of an early 1990. I did check the rear suspension and there are stock bumpstops in there (as I suspected), so swapping in some better ones is now on the list. I don't consider that a modification.

While draining the coolant, I found a couple of drips and discovered this.

Possibly related, that one bolt sheared instantly. I didn't even realize until I took the housing off. Good thing I'm tearing down the front of the engine, I can pull this off and deal with it on the bench.

Coolant looks good, though. Dad took care of his cars.

I pulled off that throttle body and put 12v to the IAC solenoid. Just a spark. We may have found our problem. Luckily, I have a spare. 

Time to pack it in for the night, I'll pick this up again soon.

dculberson MegaDork
10/31/19 9:47 a.m.

I don't know about the Miata IAC, but with my MR2 Spyder, I was able to disassemble the IAC, clean it thoroughly (I used MAF cleaner, but any low residue solvent should work) inside and then lubed it with some silicone spray and it's worked well for two years now. It had been sticking, causing a high idle. Just in case keeping the original on there is of interest to you.

Keith Tanner
Keith Tanner MegaDork
10/31/19 10:05 a.m.

When I rebuilt the engine for this car back in 2002 or so, I did keep the original engine block at Dad's request. I'm not sure keeping the original IAC is all that important at this point though :) If I didn't have a handful of good spares on hand, I'd definitely be servicing the stuck one.

It's kind of fun working on a stock 1.6 again. It's like coming home.

Keith Tanner
Keith Tanner MegaDork
11/2/19 10:28 p.m.

Finished up the timing belt job today. I was not working fast, I was mostly puttering and enjoying the process.

The thermostat neck fought me a bit. I tried welding a nut on the stub of the broken bolt, but that didn't work. I ended up drilling it out and chasing the threads. Also made sure the surface was flat and stuck the thing in the bead blaster to clean up the crud.

Everything else looked pretty good. I swapped in the new throttle body/IAC and buttoned everything up. Fired right up happily - but it still has the high idle. I'm going to have to spend a little more time chasing this down. It's acting like a vacuum leak but I haven't found it yet.

There's still a bunch to do but I have to get it off the lift tomorrow for another car. Still, some progress.

11/3/19 6:35 a.m.

Fun fact: because of the airbag thing, you couldn't import early Canadian Miatas into the US until they were 25 years old...unless they were built before Sept 1989. 

I ran into the reciprocal problem when importing a 1990 US model into Canada. The airbag instructions were not printed in French so the car was not welcome across the border. Was given like 60 days to export it. (Dad was looking forward to being the recipient of an evicted Miata!)  Used the 60 days to find a loophole.  Never even added the DRL and got away with it.



Keith Tanner
Keith Tanner MegaDork
11/3/19 5:44 p.m.

Spent a bit more time on this today. Pulled off the air valve, which is a bit of an odd way to bump the idle speed when the car is cold. Basically a controlled leak that uses coolant temperature to vary the size of the leak. A problem here would manifest itself as a high idle. Luckily, it's quite accessible. I pulled it off and everything seems to move freely. There was very little coolant in it, but after ensuring all the various lines were clear I think that's just because it's the highest point in the system and the car hadn't been run enough to burp it yet.

It's back together now. I want to get it up to temp to see how it behaves, then I'll keep poking away at it. 

Also did an oil change. I figure that drive home might have cleared out a bit of carbon. I also found some notes that indicate that I built the engine in 2002, about 80k km ago. So the timing belt service was a little early on miles, but it certainly wasn't wasted. All the parts that came off looked to be in great shape, though - pulleys, belts, etc.

Keith Tanner
Keith Tanner MegaDork
11/10/19 11:25 a.m.

The car was still on the lift and I had a bit of spare time, so I decided to take out those rear rubber bumpstops and replace them with something more modern. And here's what I found in the upper shock mounts.

That's 338's on the right and a good one on the left. These mounts consist of two pieces bonded together by rubber, and if the bond fails they can slip. The result is a drop in ride height but when I think about it, no loss in available travel. Hmm. I might have to take a closer look. You can also see the short studs on the 1.6 piece, those got longer in 1994. 

Since I'm not a fan of failed parts, I pulled a set of spares out of my boxes of parts and swapped them in instead.

I also ran into a little problem I haven't seen for a while in the rust-free southwest. The lower shock bolts go into a captive nut that's just sitting in a little cage. Get some corrosion in the mix and that cage gives up, allowing the nut to spin freely. You can usually get it off by wedging the nut with a screwdriver, but reassembly is a pain. 338 must have suffered this failure 20 years ago when I installed these Konis because the nut was loose. Here's the reassembly process I came up with - I'll have to remember this trick.

Could be worse. In more advanced cases, the bolt bonds with the steel sleeve inside the shock bushing. Then you rip the bushing apart and end up either cutting the shock apart or throwing the whole thing away. That's not fun.

I'll drive it to work this week and get a feel for the new suspension and see if I can diagnose that idle.

Keith Tanner
Keith Tanner MegaDork
11/11/19 11:24 a.m.

Road test! The Mini decided to be a little cranky, so 338 got the nod for running errands on a beautiful Sunday. The rear suspension feels good with no noticeable bottoming at all thanks to the new stops. I'm happy with that. I think the rear shocks might be getting a little tired. I'll turn them up a bit. I figure I'll address the fronts when I do bushings, as it's higher effort to pull the front shocks. There's a bit of harshness up front that needs to be sorted out.

Also, you can pack a reasonable number of groceries in a Miata trunk if you're careful :) Well, reasonable if the entire family fits in said Miata.

I also took it to work today so I can put the smoke machine on the intake and check for air leaks. I think it has to have a big one somewhere. The car will currently cruise at 50 mph in 5th gear with my foot off the throttle.

Keith Tanner
Keith Tanner MegaDork
11/13/19 8:39 p.m.

WOOOO! Victory!

I cornered Bill Cardell after a meeting on Monday and told him about the problem. Bill has a mind that, if you load it with a problem, will chew away at the problem as a background process and pop out an answer at some point in the future. He is the king of the weird diagnoses.

But that wasn't needed this time. I'd been starting to focus in further on the air valve on the intake manifold or a massive air leak as the culprit and that's where he went as well. There were also some questions about why the idle fuel cut wasn't kicking it - it shouldn't rev past 2500 or so with a closed throttle signal.

So, diagnosis time. I'd already pulled the air valve and confirmed the piston was moving (see my 11/3 post), but hadn't really done much more than that. I started by checking for a big fat air leak.

I get accused of having access to tools that normal mortals do not. Usually this is untrue, but today that is not the case. 

The disco smoke machine revealed no leaks. Checking the TPS for a closed idle signal indicated that it was indeed registering - I'd been careful to calibrate that when I put the new throttle body on.

So it was time to go to the Idle Air Valve (IAV) again. I'd looked for a spare in my stash of parts, but come up empty. I probably found four air flow meters including one that is from another application (GTX?) as well as at least one more throttle body, but no IAV. FM didn't have any. However, I do have another couple of 1.6 Miatas in long-term hibernation in the shop, so I popped one off my first car.

That's 338's on the left. You can see the piston in the lower hole - they should be in the same place on both valves. If I try to blow through it, I can easily blow through 338s but not the other. Culprit found. Bolted the good one back on and the car was healed. I'd never really paid much attention to the IAV in the past. That piston moves with temperature to provide a higher idle in cold temps. Seems awfully crude, but EFI was a lot cruder back in the late 80s. Heck, Honda was still putting carbs on any car that didn't have an Si badge. We forget.

I also happened to have a set of my favorite LED Nighthawk headlights sitting around. 338 was running a set of Hella H4 housings with bulbs that had a few years on them. I have more bulbs - so many more bulbs! - but I have become enamored of good LED headlights so I swapped them in. They make an NA look even more adorably derpy than normal headlights. What's not to love?

Keith Tanner
Keith Tanner MegaDork
11/24/19 7:00 p.m.

Update. I had the car out for some fun in the sun yesterday.

I installed a very important part today. Hydraulic hood lifts are one of those things that seem unnecessary until you install them, then you wonder why you waited. The hood opens further, the prop isn't always in your way. It's luxury. I won't tell you where I got these, but you can probably guess :)

I also added a little touch that makes me smile. The 1.6 cars had this Mazda logo from the factory. It's gone on a lot of cars because of repaints, and it's NLA. You can see from the paint that this bumper has some history, so the sticker was long gone. I cut this one on our vinyl cutter. One of my cars still has the sticker so I was able to locate it correctly.


The idle still isn't completely happy. It's almost like the new air valve is better but not quite right. When cold, idle is normal. When hot, it's just over 1000. I have a new valve coming (I stole the one I'm using off a spare car) so we'll see what that does.

Also, when I opened the hood to install the struts, I found this. It looks like it might be one of the lines attached to the thermostat housing dripping on to the PS belt. It's not a big leak, but I'll need to sort it out. I cleaned that fitting out when I was chasing the idle problem, I'll take another look at it.

The car doesn't have 100% smooth power delivery. I think I'm going to pull the injectors and have them cleaned, as it feels like inconsistent fuel delivery to me.

Keith Tanner
Keith Tanner MegaDork
12/26/19 8:56 p.m.

338 hasn't been doing much of late because I got distracted by taking the MG apart and then buying a Cadillac. But in the process of shuffling cars around, I realized that I would like this car with a hardtop, and I have a car with a hardtop that I'm not using. Yes, I forgot about a spare Miata hardtop.


Good ol' 50590 donated the top. That's my first Miata and my first car overall. That hardtop hasn't been off the car in probably 15 years. The top was a little tight to put up. The ORIGINAL 1990 top, although the rear window was replaced in 1992 after it broke when the top was dropped in cold weather. Canadian cars don't see a lot of UV :)

But the real problem is those stripes. Vinyl. I put them on in 1996. Oy.

This is not going to be fun. Right now, I'm using plastic scraping tools and a heat gun. Any other ideas?

codrus UberDork
12/26/19 11:21 p.m.

3M makes a wheel for removing stickers/adhesive, you put it on a drill and it's supposed to be paint safe.  I've never used one, but I've heard good things.


MrChaos SuperDork
12/27/19 5:58 a.m.

i think the issue will be the color difference between the stuff under the vinyl. especially mazda single stage red from 92

Keith Tanner
Keith Tanner MegaDork
12/27/19 10:30 a.m.

I’ve talked to a coworker who’s used one of the eraser wheels. It won’t work on the body of the stripe but it’ll take care of cleanup. They’re really for pinstripes. 

We’ll see about the color shift. In my experience, that red comes back pretty darn well if you put some work into it. It’s not an issue anyhow, because I only have one red hardtop so it’s the hardtop I shall use. 

AngryCorvair MegaDork
12/27/19 11:35 a.m.

In reply to Keith Tanner :

Got one of those little 500W halogen work lights? If yes, that may be easier to work with than the heat gun.

Keith Tanner
Keith Tanner MegaDork
12/29/19 5:19 p.m.

Angry for the win! It's still not a fast procedure, but it's faster!

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