Tickover

Tickover

The revs should be the same in ‘normal’ and ‘service mode’

Putting the paperclip in... (Shorting terminal A and B of the (ALDL) Assembly Line Diagnostic Link)... while the engine is running at operating temperature puts the car into “service mode” (CO Adjustment Mode)

Locate the idle adjustment screw on the top of the throttle body. Have a flat screwdriver handy. With the engine up to temperature and running, put the paperclip in. If there’s a problem with the base tickover it will rise or fall as the clip contact is made. Adjust to 950RPM – rev the engine slowly to 2000 and back – check and adjust the revs if necessary – remove the clip - rev the engine slowly to 2000 and back – if it’s still 950RPM the job is done, if not, repeat the process. Only make the adjustment with the clip in.

In order to prevent the adjustment moving on its own over time, here's a simple modification using an ordinary tap washer and a small screw.