JBL GT5-A402 Install & Review, sorta

When I bought my Miata back in June, the audio situation in the car was pretty dire. An aftermarket Pioneer head unit with possibly the worst front interface I have ever seen was rattling around in the DIN slot. The previous owner asserted without much confidence that it was indeed in working order. I turned it on, it sounded like it was shorting across the speaker outputs, so I turned it off and never turned it on again. Honestly, the stereo system is really at the bottom of my priorities when buying a used vehicle. The number of clean aftermarket installations are sadly outnumbered by various levels of clusterfuckery ranging from simply cheap components often inferior to stock (which it seemed I had encountered) to hacked up harnesses complete with a rats nest of unlabeled and severed wires.

So I paid no attention to it, and after I discovered that the head unit was held in place by nothing more than the force of gravity, I yanked it out. It was just so much dead weight, anyway.

I toyed with the idea of removing the remainder of the stereo. I didn't want to dedicate a huge amount of resources or accrue a large weight penalty by putting a monster stereo in the car. Besides, that goes against everything the Miata stands for. On the other hand, I wasn't sure I could get adequate performance from simply a head unit and door speakers. It's not quiet in the Miata cockpit.

So, rather than a head unit and an amp, I decided to skip the head unit completely and just use one of the many MP3 players I have lying around. Hey, head units are heavy. I decided on the JBL GT5-A402 for the amp because it was a) two-channel and b) cheap. But, importantly, not ridiculously, awfully cheap. There aren't any absurd and unrealistic wattage ratings on the casing and it comes from a big (very big) and reputable manufacturer, Harman International. In this case branding means it won't be completely crap.

Honestly, the hardest part of this install was getting wires figured out. Yes, the harness had been mutilated. Once that was done the rest of it was surprisingly easy.



There's a tunnel that runs from the trunk to the passenger compartment, and since the battery is mounted in the trunk, the install is almost trivial. No drilling in the firewall.



The amp went behind the passenger seat. Note that if you have a post-1994 NA, the ECU is mounted here. I think. Someone correct me. Either way, make sure what you're drilling into.



I was expecting to find stock speakers in the doors, but it looks like someone put in these poly cone Pioneer units when they installed the head unit. If they're installed with the same level of skill as the head unit, there are wires twisted around the speaker terminals and wrapped in electrical tape back there. At the moment I'm just going to leave them. They don't actually sound too bad, and I haven't figured out exactly what I want to put in the door yet.



I know this install is neither unique nor revolutionary, especially in the Miata world, but I am still pretty happy with it. It fits the Miata ethos. Functional, minimally complex, and light. The amp is very slightly heavier than the head unit that got binned, but I excised about three feet of tangled up wiring and three (yes, three!) inline fuse holders. At the very least, I've reduced the risk of my car burning to the ground in an electrical fire.


As for the amp itself? I didn't tear it down to check out the quality of the components or the packaging. I don't have reference quality speakers to listen to it critically. I can say it has way, way more power than those particular speakers need. It's not supposed to be a flagship amp - I paid $80 for mine - but I'm confident it'll deliver its rated output with a minimal amount of distortion. I've been impressed at how much detail I'm hearing even with the poor speakers and the large amount of cockpit noise. The screw terminal block could be wider and beefier but it's not exactly flimsy. The included mounting screws are the perfect length to mount through about half an inch of insulation and carpet. They aren't self-tapping. The amp has a nice soft turn on feature, but that's hardly ground-breaking or upmarket these days.


So, for a total of right around $100, including the mounting kit, I've added two 60 watt channels. Is it going to win any competitions? Well, I hope not. Does it go louder and cleaner than any head unit? Absolutely. Combined with an almost infinite playlist, the fact that I don't have to carry expensive and obnoxious media, and the fact that it looks like my stereo has already been stolen - this is an unbeatable upgrade for the working Miata.

Miata 'Ebay Clears' turn signal install

Well, the stock turn signal / running lamps at the front of my Miata were starting to show their age. As in they had huge rock chips and holes and were full of rusty water. One of them was starting to short out in heavy rain. Not good.

OEM replacements are $80 apiece. While I really do appreciate the factory look, I can't see spending $160 on a couple of molded plastic pieces. I really just wanted a functional replacement for the factory pieces. Well, the aftermarket knockoff hucksters on Ebay would be happy to sell you a pair of clear (or smoked - out of the question for this car) turn signal lamps for $30.

For the pair. With bulbs.

I have to say I was skeptical. Would they leak? Would they have fitment issues? Well, no. They may be slightly cheap, but they're totally solid. Proper venting in the back. The pigtails and connectors fit perfectly. I have to say I'm impressed. Worth $30? Absolutely.

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.

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.

Trouble...

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