Mazdaspeed Miata+Knocking?

Howdy all:

So, I sold my old Subie, joined the Air Force, now I have a steady job and live in California (for at least the next year and a half). I'm at home now on leave for Christmas and I'm investigating a used '04 Mazdaspeed Miata.

I've always wanted a Miata and the MSM is particularly exciting to me. There are a few other Miatas in the area that I'm considering, ranging from a base '99 with no power nothing to a '03 SE but this MSM is my first choice.

I took it for a test drive today and a few things bothered me: one is the fact that it was on the original tires and they sorely need replacing. But the main problem crept up less than 2 miles into the test drive, when the check engine light came on, started blinking and the engine began to run very rough. This would happen when the car was in a higher gear (3 or 4) and I would floor the accelerator. It go so bad the car would shudder and buck around. At first I thought it was a clutch problem, but this car has only 21,000 miles on it and otherwise appears to be in great shape. It would also begin to randomly idle very rough after idling smoothly at a stop for a few seconds.

When I got back to the dealership, the salesman helping me talked to his manager about it, and although I didn't hear it first hand the manager said that one of the technicians accidentally put 87 octane in the car, and that it was developing a knock. That did make sense, but I'm still skeptical. We agreed that they would change out the gas and I'll test drive it again on Monday.

Am I falling into a trap? The car isn't very reasonably priced and I was going to offer fair market value for it, so I may avoid buying it in the first place. But if there's some serious trouble then I'm walking away and not looking back.

Any and all advice is appreciated

tl,dr: I checked out an MSM, needs tires, engine shudders in certain driving conditions, and randomly at idle, dealer claims it accidentally put in 87 octane and that the car will be in ship shape on Monday.

Walking away is always an option. I'd check the car very carefully to make sure it hasn't been poorly modified - the MSM has some pretty good survival instincts to prevent yahoos with a Home Depot boost controller from blowing things up, but there's enough info out there to bypass the safeties.

Idling poorly isn't an octane problem, though. Find out exactly what that code is (the number, not just the "oh, that was from excessive knock") and check it. There may be a fuel delivery problem.

Or just walk away. If there's no particularly redeeming attributes to this particular car, that's always a good option.

My MSM runs fine on 87 octane. I tried a few tanks in a gas mileage experiment a few years back when gas prices were through the roof. Like other modern cars the ECU just retards the timing if need be and there is nothing dramatic that happens at all. What you describe is not normal.

Keith, thanks for chiming in so soon. I may ask the dealership on Monday for the exact code, but if T.J.'s experience is accurate, then it sounds like there are other problems. We'll find out tomorrow.

find another car........ it's not like that's the only Miata on the market... there may even be one or more for sale on this forum... from some one less likely to screw you than a stealership will, plus be more honest and forthcoming about any potentional trouble areas

T.J. wrote: My MSM runs fine on 87 octane. I tried a few tanks in a gas mileage experiment a few years back when gas prices were through the roof. Like other modern cars the ECU just retards the timing if need be and there is nothing dramatic that happens at all. What you describe is not normal.

Keep in mind that it will only retard the timing if there is knock, and I don't believe there's a long-term trim. So you'll have some knocking before the car retards timing and this will happen all the time. It's not a good plan. A good way to get home if you get stuck in the middle of nowhere, but I'd recommend running premium whenever it is available.

In reply to wbjones:

True dat, but this IS the only MSM in the area, and I've been wanting an MSM for a couple of years now. I won't lose sleep over it if I have to get a different Miata...'cause I'll have a Miata! But still, it'll irk me a bit, you know?

OrangeRazor wrote: In reply to wbjones: but this IS the only MSM in the area

Widen your search area. Look south for a better chance of getting a rust-free example. Plane tickets are cheap, and I hear Florida is lovely this time of year.

Miata's, even MSM's, are plentiful enough to skip one if you're unsure on it. Broaden your search, wait a little bit, but I think I would skip this one.

I would say buy one out in California or one of the western states to avoid any problems with rust.

Unless they are willing to take the MSM to a Mazda dealer and give you at least a limited warranty, RUN, dont walk, away.

I've had a 2004 MSM for over two years now, and the only problem it's had is similar to the one you described. It turned out to be a 3-way solenoid vacuum switch connected to the MAP sensor that gets fouled up. Apparently, the MAP sensor doubles as an atmospheric pressure sensor depending on whether the solenoid is energized. Imagine how confused the ECU could get if it sampled atmospheric pressure and got manifold pressure instead (or vice versa). Do some Googling and search on the Mazda-Speed forum for better info than I've given. This is a fairly common problem referred to as "the bog". I now carry a spare solenoid ($60) in my glovebox.

It's possible the problem lies deeper.

In reply to Keith:

I did it for a couple tanks in the winter time. There was no detectable pinging to my ear. I've used premium for the other 50k+ miles. Good to know info about how the system works - thanks Keith.

Thanks for all the advice, guys. If I could expand the search area I would, but after test driving a couple other Miatas I've decided to go in another direction...but now I have a different conundrum!

New Thread