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Old March 13th 11, 04:17 AM posted to rec.autos.makers.mazda.miata
KWS[_2_]
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Posts: 16
Default 1997 P0300 weirdness

On 3/12/2011 9:41 AM, Hal wrote:
> All - my 1997 with 109k on the clock has developed an annoying habit
> of flashing the CEL at highway speeds recently. I never lose any
> power, and the car runs fine throughout the RPM band.
>
> I found a TSB regarding this issue and checked the gap between the CKP
> and the crank sensor plate. It was out of spec, so I adjusted it. I
> also cleaned all three grounds in the engine bay and reset the light.
>
> The problem came back. The only other thing I can mention is that my
> speedometer cable broke a few months back because the speedometer
> itself locked up, so I took the speedo apart, oiled the bushing, and I
> repaired the cable with a small piece of model airplane all-thread.
> The speedo works now but the pointer is a bit jumpy because the end of
> the cable is not perfectly straight. And while I was in there fixing
> the speedometer I noted that there is a reed switch on the magnetic
> drag ring that is probably the feed to the computer for the vehicle
> speed.
>
> So..going out on a limb here.....does anyone know...do the VSS and CKP
> sensors work in tandem to detect misfires? If so, I may need to
> replace the speedo cable to fix this problem....
>
> Thanks,
> Chris


The first thing that comes to mind is the tendency of Miatas to eat
spark plug wires. If yours haven't been replaced in the last 30K miles
or so, you might want to throw a set at it and see if that makes the
problem go away.

On line, I found this. The assumption is that a P030X code might be a
number where X is 1 to 4 if a specific cylinder is affected:

"Random misfires that jump around from one cylinder to another (read:
P030x codes) also will set a P0300 code. The underlying cause is often a
lean fuel condition, which may be due to a vacuum leak in the intake
manifold or unmetered air getting past the airflow sensor, or an EGR
valve that is stuck open."

If it was me, I'd do the plug wires first if they are getting due for
replacement.

Good luck; let us know what you find.

Ken
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