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Mazda MX5 NB, Engine Cleaning

There isn’t a much greater, simple pleasure in life than doing an Italian Tune Up on a car.

I can confirm that even with the backup battery removed from the siren, the alarm will trigger and sound when the car battery is reconnected. Ask me how I know…. glad I was prepared and had the remote in my hand.

With the battery reconnected, the ECU has now been reset. Starting the car up took a few cranks and it ran really lumpy and angry. Not on all four cylinders, that’s for sure. It was also blowing black smoke out the exhaust, so very rich.

A few sharp jabs of the throttle, and it settled down and started to idle a bit nicer.

On the initial drive the engine felt a bit punchier, who knows what fuel the previous owner was running so it might have been pulling timing to compensate. Once the engine was warm I shot back home and set the base idle.

Setting the base idle is easy, but you need to remember to short two pins in the diagnostic connector, or it wont work properly. The two pins you need to join are TEN and GND (in other words, short TEN to Ground). I used a straightened out paperclip.

The idle will generally change when you short the terminals. What you’re aiming for is no change, so that the idle is the same whether the terminals are shorted or not. Mine raised up when shorted, so I used a small screwdriver to tweak it down. The adjustment screw is accessed from the side of the throttle body, above the left hand nut at the top in the picture below.

I still have an issue with the rpm randomly dropping to about 2-300rpm, almost stalling and then recovering to normal rpm. Need to look into that, was hoping this would fix it but it didn’t.

The next thing I tried was to use a can of Mitsubishi Shumma that I had kicking around to give the internals of the engine a clean out. This is a hardcore foaming cleaner that Mitsubishi dealers use to clean out carbon in the intake manifolds of diesels and GDI engines. Similar to Subaru Upper Engine Cleaner too. I have mentioned this stuff before, when I used it on the S401.

I pulled off the vacuum hose that’s just behind the throttle body on the top of the inlet manifold, sprayed about quarter of the can in with the engine off, left it a couple of minutes and then started the engine. It was hard to start as expected, but eventually started and ran fine. Not much smoke.

The smoke came when I started to squirt the cleaner into the running engine. I had to hold the RPM up as it went in, and the plumes of smoke were quite impressive. In my experience, the dirtier the engine, the more smoke…. so this one was bad.

To finish off the cleaning I needed to take the car for a drive, get the engine hot and give it an Italian Tune up…. or basically thrash the pants off it for a bit. Lots of high RPM work.

Off came the top

And off I went. Oh how I have missed driving a topless car. There is just something about it. The feels, the smells, the sights, it’s all good.

I took the car for a good trash around some back roads, making sure to keep it well in the top end of the rev range. It loved it, and now the car is running better still, and smoking a lot less at high rpm.

Unfortunately it’s not perfect, I still need to track down the idle issue and it’s still not running 110%. I checked the spark plugs again after the Tune Up and they are still black as anything, so they need to go. I’ll grab some new ones tomorrow.

I’m getting there. I still can’t believe the previous owner claimed there was nothing wrong with the car 🙄

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