The fun part about cheap Miatas is that they all come with their own set of challenges! It seems like I am starting a rescue service for unloved Miatas. The most recent is a 92 that followed us home. It is pretty solid for an Ohio car, has fairly small holes on the rear rockers, but otherwise very little rust. Actually we can call this a "rust free" car because the PO cut out all of the rust! The new metal just wasn't welded back in! Still not bad for an $1100 Miata w/ a hard top.
But I digress... The reason for this post is that said Miata is running like crap! It feels like it is running on 3 cylinders (and it probably is). I know that the compression is down on the #3 cylinder, but it seems to have other issues. I knew that the timing belt had been replaced, so I pulled it apart and checked to make sure that it isn't off a tooth, it's fine. I have changed the ignition wires and checked the plugs. Adjusting the timing doesn't seem to help. I still need to replace the fuel filter.
It is showing fault code 9, which is the Water Thermistor. The only time that I have had to replace a thermistor on a 1.6 car it was causing it to run poorly, but not this bad. What effect should I expect from this problem?
Any other ideas on things to check? I have access to another 1.6L car, so I can swap sensors without having to buy new ones. Where should I start?
Well, you've got a known bad component and you can replace it for free. Try replacing it and we'll go from there.
Keith wrote:
Well, you've got a known bad component and you can replace it for free. Try replacing it and we'll go from there.
Yeah, I guess I should have seen that coming! I was curious about how much of an effect the thermistor could have.
I'm going to go out on a limb on this one. A failed sensor could have no effect or a very large effect. I'm confident this is true.
Thank you very much! Or maybe not! 
What is it with Miatas and plugs and wires?!!!
I replaced the coolant temp sensor, and it didn't help. No big deal $18 for the sensor and it needed to be replaced anyway. Bought the fuel filter but before I jacked up the car I decided to go ahead and replace the plugs even though when we pulled them earlier they looked fine.
When I got to the plug in cylinder #3, the one with low compression, I noticed the the old plug came out with 2 washers on it! Looks like the washer from the plug before this set had come off in the hole. I was hopeful that I had lucked into the problem, and when I fired it up, it was smooth as silk!!! I guess it is better to be lucky than good! My guess is that this little washer has been confounding the two previous owners, as the car was a project that had been given up on twice!
To quote someone from another post, now it needs an "Italian tune up" and I think it will be as good as new. I haven't redone the compression test but I suspect that this could also have been causing the compression leak.
WOO HOO!!
I'l take it off your hands for you (especially since it is running better now)
Sure, but with all my free labor the value has doubled! Just wait til it's painted! 
