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Re: Pull Fault codes on '89 100? Out of luck?

At 11:42 AM 7/31/97 -0400, Jeff Wolf wrote:
> Hello esteemed list:
>I am trying to diagnose and fix a intermittent low idle problem.  Car has
>122,000mi on it and about 75% of the time Idles at about 600rpm with the A/C
>off.  When A/C comes on it drops down to about 400.
>I have access to a bentley for the '88 5000 which goes into detail on how to
>pull and read the codes for the CIS-III cars but when I try to follow the
>procedure (engine running, fuse into Fuel Pump relay for 4 seconds, remove)
>I don't get any flashing light.  None, Nada.  The owners manual seems to
>indicate that the "Check engine" light might have only been put on
>California models.  Is there another way I can read the fault codes?

You can no longer read fault codes thru the fuel pump relay after 1988.
You can do it by accessing the new connector in the footwell....look in the
archives, it was re-posted maybe a month or so ago.

>Anyone have any ideas about the idle problem?  I'm leaning towards the Idle
>switch or wiring to it being bad.  When it idles correctly at about 750, the
>a/c is correctly compensated for, i.e. the idle stays at about 750.

You've got a problem in the idle stabilizer circuit.  Your symptoms are
what happens when the computer loses the signal from the ISV and goes into
default mode (this will set a code, so pulling the codes is crucial).  It
could be a wiring problem to the ISV, a vacuum problem in the hoses going
to the ISV, etc.  Check the connector to the ISV carefully - I currently
have one on an '88 90q that develops a wiring fault when the engine is hot,
producing your same symptoms.