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Mazda MX5 NB, MAF & Idle Valve Clean

Since obtaining the car its been running very rich, pouring carbon out of the exhaust and blowing plumes of black smoke. Today I had a look to see if I could fix it.

I mentioned at the end of yesterdays post how bad the carbon out the exhaust was, it leaves trails on the ground behind the tail pipes and coats anything behind the car. It also blows quite a large amount of black smoke at high RPM and just doesn’t feel quite as sharp as it should.

There are a few things it could be, the most common being a dirty Mass Airflow Meter (MAF). This is where I would start looking.

Because life can be a prick, I mentioned yesterday that I don’t have a key for the alarm siren. My first task today was to fix that issue so I could disconnect the battery and reset the ECU after my cleaning.

The siren is hardly hidden, or wired in well. I think the insulation tape I point out in the video running down the inner guard was actually to hold the bonnet switch wiring up. It ceased doing that long ago, so I removed the tape.

I tried option B, which was to pick the lock but I got impatient when it wouldn’t work (having never picked a lock before I’m hardly experienced at it), so went to option C, disassemble and see what I can do from there.

This is also a good warning about siren placement, as it’s really not hard to open the siren up and disable it. First step is to use a small flat blade screwdriver to pull as much of the sealant out of the screw holes as possible. With that done, it was as simple as using one of my JIS screwdrivers to easily remove the screws. Note super technical tool to stop siren dropping down as I was unscrewing the screws.

And then it just kinda falls open

Does not show a lot. Not sure why there appears to just be a bunch of weights inside the siren, behind the speaker.

Remove the central screw and you get access to the goodies

That big green cylinder is the backup battery. If power is cut to the siren, this battery will make sure your ears still bleed. My plan initially was to just snip the siren wires, but removing the battery was an even better idea. This makes it like a cheap alarm that doesn’t have a battery backup siren. The alarm will still sound, it just wont have battery backup anymore (and means I can disconnect the battery freely). It’s a shame to lose this function, but I had little other choice if I didn’t want to spend money on it.

With the battery removed, a quick test shows that the siren still works properly, so I reassembled and moved on.

The MAF is the little box in the intake piping, behind the air filter.

Removing it is as simple as disconnecting the wiring, and loosening two hose clamps. I used electrical contact cleaner by CRC to clean the sensor. Just hose it in and try to aim for all the bits sticking up in the middle. Hose it from both sides and all angles you can.

Since the intake was coming apart, and I have been having issues with the idle, I removed the throttle body and idle valve. The throttle body is held on with two nuts at the top, and two long bolts on the underside.

The throttle body was filthy, especially around the passages for the idle valve

Two screws hold the idle valve to the underside of the throttle body

I soaked the idle valve in degreaser and brake clean to get all the carbon and oil out of it

It was quite bad, lots of buildup inside.

Once clean, I cleaned the throttle body inside and out, and reassembled.

I quickly whipped a couple of plugs out to inspect their condition. They look OK, obviously VERY carboned due to running rich but the gap was OK. I think they need replacing anyway due to being borderline fouled. They wont be helping.

Leads look fairly new. Theyre NGK, so not standard.

Since I was already in the garage under the hood, I also did some nosing around. Under the 710 cap looks good, nice golden sheen, no obvious sludge. The other good news is that the front oil leak might be just the valve cover gasket. It’s certainly running down the block from the front corner. The oil on the front starts way above the crank seal level.

So did all this work do anything? Yes. I took it for a spin, and its feels more lively, and isn’t blowing anywhere near as much smoke at high RPM anymore. It also doesn’t paint the ground black when you rev it up stationary.

I still need to reset the ECU and then set the base idle, that will be tomorrows job. In preparation for that, I need to disconnect the battery. You know how I “modified” the siren? Heres the test.

I disconnected the negative terminal, and suddenly the siren goes off; a quiet “BLOOP” and then silence. Seems the siren has a capacitor that was just enough power for a bloop, and then it died. A great success then.

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1 month ago

Useful tip on cleaning the MAF, thanks.