From JE Robison's site:
Code 48 - Stepper motor
Check base idle speed as follows:
First remove and clean the idle motor and the port it screws into. Clean the throttle body as well.
On the top of the throttle body you will see a hole (possibly covered by an anti tamper plug) for the base idle adjuster.
Remove the air bypass hose from the throttle body, which will cause the engine to speed up to 2500rpm or so. Unplug the connector to the idle motor after 5 seconds then reconnect the hose.
Squeeze the hose shut with needle nose vise grips and adjust the base idle using an allen wrench to give an idle speed of 6-700rpm. Get the lowest speed you can that gives smooth running and does not stall when blipping the throttle. Screw in for slower idle, out for faster idle.
Reconnect the idle stepper and remove the vise grip and you should be done.
In addition, refer to tests 15 and 16 of continuity test procedure. Check road speed sensor- refer to test 25 of continuity test procedure.
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