Re: [DML] Eratic engine idle when warm

["Walter Coe" <Whalt@xxxx>]

> 1. Could there be something wrong in my Lambda circuit causing this
> such as a bad O2 sensor?

That isn't the first thing I would check. But to check this anyway, unplug
the O2 sensor. This should(*) cause the ECU to assume that the sensor
hasn't warmed up yet and will instead use its preprogrammed maps. If this
stops your RPM fluctuations, then you have a faulty O2 sensor. About my
(*), I'm going by what I've read in books and on the DML, but I have no
hands on experience doing this test, so I may be wrong.

> 2. Could my frequency valve be bad?

Not likely, but I think you could be close. I would look for bad electrical
connections. Unplug the connector going to the FV and look for corrosion
there. Also check that you have a clean ground. This is on the vertical
surface of the intake manifold just to the left of the FV. If your
fluctuations in RPM are intermittent, then suspect a bad electrical
connection somewhere. If it is rhythmic, then uh... gee, ... I dunno. That
is somewhat normal on these cars but not to the degree that you are
experiencing. Also check that your idle speed switch is connected and
working. Your idle should never reach 10000 RPM. Also check the electrical
connection to your idle speed motor the same as for the FV. I once had a
corroded connection on my FV which caused the volume of the buzz to change
as I giggled the connector. So since you hear changes in the volume of your
FV, I suspect that the cause of your problem is similar. It is only the
duty cycle of the signal to the FV that changes -- not the amplitude.

The next time you experience these symptoms, check the voltmeter in your
instrument cluster. It's not likely, but perhaps you have a wimpy Ducy
alternator that allows your battery to deplete by the time the engine warms
up. That is if you are allowing the car to sit at idle until it warms up.

Walt Tampa, FL