94 Buick LaSabre Hi Idle and no Speedometer

[Bob Valentine]

The high idle could be due to a lot of things.   No or incorrect IAC
control for some reason is most likely the cause, and the VSS has a lot to
do with idle.   The park/neutal switch can also get involved, as could a
major vacuum leak.

In the '747 TBI ECM the ECM resets the IAC motor over a certain MPH so that
the ECM knows where "0" or full in is.  No VSS and it eventually doesn't
know where the IAC pintle is at.     No VSS on a '730/'727, decel idle and
idle in general can get wierd since the ECM doesn't know if it's
transitioning from movement to stop or vice-versa.

So given that the high idle coincided with the speedo not working, it's a
good guess to start with that circuit and it's related parts.   

-> Bob Valentine
-> bob at tecmark.com


At 11:00 PM 8/27/2001 -0300, you wrote:
>So why would his engine idle high? (that's another story i'm guessing).
>
>Sounds like some odd ECM problems.
>
>Shannen Durphey wrote:
>
>> Russ & Renee Pelfrey wrote:
>> >
>> > I have a 94 Buick LaSabre 92k miles 3.8L engine, OBD-1 compliant but
with OBD-II Connector.  The pin outs used in the connector are 4,5,8,9,14,16.
>> >
>> > Problem:
>> >
>> > Last week the Ser. Eng. lamp came on and the speedometer stopped
working along with the cruise control.  Also, the engine idles very high.
prob. at about 3k rpm.  I have replace the VSS to no avail. Please advise,
I don't want to pay $600 for 30 min and a $50 part.
>> >
>> If you know of a shop that's charging $1200/hr as a labor rate, please
tell me.
>> I need to pack up my tools and change jobs.
>>
>> You will want to invest in a good service reference, which can be
anywhere from
>> $15 to $75, depending on what manuals you get and where you buy them from.
>> You'll want to get a good multimeter, which typically costs around $300
but can
>> be as high as $600.  You'll want to dedicate the better part of a day
because
>> electrical problems can be anything from a 5 job to something that
requires in
>> excess of 6 hours to find.  If you have more experience the problem can be
>> easier to find, but I think you may want to "spend" the entire day for this
>> problem.  I can't put a dollar amount on that, but you I'd expect that
you make
>> at least $10/hr so we can say the value of your time is no less than $60.
>> You'll also want to have miscellaneous hand tools around for electrical
repairs,
>> parts replacement & etc which will add to the cost of doing the job
yourself.
>>
>> Remember that the above list includes the tools that a professional
mechanic
>> needs to be able to fix a car that comes into his shop, and remember
also that
>> the shop he works for needs to charge enough to stay in business.
>> Remember also that the repair businesses which you are trying not to pay
are the
>> very reason that there are people around who have the information you
need to
>> fix your car.
>>
>> With that said, it sounds like you have no speed sensor signal.  You
will want
>> to use a scope or multimeter to see if the speed sensor you've installed is
>> generating a signal.  The signal is an A/C wave which will change in
frequency
>> and voltage as tire speed increases.  You can lift the car onto
jackstands and
>> place it in gear to check this.  If you have no signal from the speed
sensor,
>> you'll need to physically remove it and check to make sure the
drive/driven gear
>> or the reluctor ring is ok.  If you have a signal at the sensor, you'll
want to
>> check for a signal at the ecm.  This is where the good service manual will
>> really help.  You'll want to use your meter or scope to check for a signal
>> similar to the one you saw at the vss.  If no signal, you'll probably
want to
>> check the wires from the vss to the ecm for opens/shorts.  If you have a
signal,
>> you'll want to check the terminals in the ecm connector and in the ecm for
>> damage, misalignment, corrosion, and generally poor condition.  If
everything
>> checks out, the odds are pretty good that you have a bad ecm.
>>
>> But all of this could be untrue because GM sometimes sends the speed
signal to a
>> buffer box or to the instrument panel before the ecm.  So you'll really
want to
>> look through a factory service manual or another good reference to see
how the
>> vss is wired up.  You can use the Alldata web site
>> http://www.alldata.com/vehicle_owner/index.html
>>
>> to locate an Alldata shop near you.  They often print up schematics and
>> diagnostic pages for a small fee.
>> Shannen
>>
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