I went to Auto Zone and borrowed their code reader to find out what was wrong with my 2002 Mazda Miata. I had (2) faults, P0304 (missfire #4 cylinder) and P1518 (VTCS vacuum solenoid failed open). What the heck is a VTCS vacuum solenoid and how do I fix it? And are the (2) faults related? I've never used a code reader before and am not sure on how to interpret the information it gave me.
Somebody help please?

dpags

 

Hi Dpags,

It's funny: my 2001 Miata is throwing the same code!

So I've been researching it as well. I ran across a good thread on this topic in MiataNet:

http://forum.miata.net/vb/showthread.php?t=145808

This driver ended up replacing the solonoid altogether, at a cost of $168 for the part, which he ordered from Trussville Mazda.

It's interesting that the code explanation he got, and I as well, had to do with a so-called intake manifold runner valve, but the actual part he replaced is the one that is mentioned in your error description. I imagine the difference arises from user generic code-reading devices versus those that are loaded with custom data pertaining to Miatas.

For now I'm taking a "wait and see" attitude, because the engine is doing perfectly, power is unchanged, gas mileage is the same, and because this code doesn't come on when restarting the engine after it is fully warmed up.

For background, I have a Scangauge II, a great device for general info and also instanteneous and average gas mileage readings. These data I use to tweak my driving style when I don't want to go all out. The Scangauge allows allows me to reset any codes--something which I've had to do repeatedly with this P1518.

I downloaded the Miata 2001 service manual and will start digging in it once the weather warms up and I can attend to the engine with some degree of comfort. (Living in New York City, I park on the street...)

Best,
Michael Kappeyne