Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

Symptoms of Failure:
High idle at startup or uncontrolled idle above 750
rpm.
Diagnosis:
This switch is a simple device: at either extreme of
motion, an internal switch is closed and you will
see continuity between one outer connector and
the middle ground connector. Disconnect the
switch connector and jump from one side
connector to the middle ground connector. If idle
returns to normal, then the switch is at fault. The
switch is not repairable.
Adjusting the TPS:
To adjust the TPS:
Throttle Position Switch, Courtesy
FCPGroton
1. Remove the throttle body from the car and loosen the TPS adjustment screws
2. Hold the throttle plate and keep it from moving. Rotate the TPS clockwise, then
counterclockwise until a click is heard. Continue rotating until it stops but do not cause
the throttle plate to move. Secure the screws
Proper adjustment is obtained when you open the throttle plate and insert a feeler gauge
at the throttle stop screw:
❍ When you close the throttle against a .45mm feeler gauge, no "click" is heard from
the TPS
❍
Oxygen Sensor
When you close the throttle against a .15mm feeler gauge, a "click" is heard.
Theory and Operation
1. Oxygen sensors should last over 100k miles under ideal conditions; various contaminants
will shorten that considerably. For testing procedures and other info see:
http://www.f-body.org/oldfaq/html/tech/sect2.html#oxysensor
2. [Excerpts from Underhood Service magazine, Nov 2000, et al]
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in
the exhaust as it exits the engine. Monitoring oxygen levels in the exhaust is a way it gauges the