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Lotus Service Notes Section EMN
Page 13
EMN.10 - THROTTLE POSITION (TP) SENSOR
The throttle position (TP) sensor is a potentiometer fitted directly to the end of the throttle spindle, and
provides the ECM with information on both throttle opening, and rate of change of throttle opening. For
example, when a fully closed throttle and appropriate engine speed is signalled, the ECM activates the idle air
control valve to regulate idle speed; a rapid or sudden opening of the throttle will initiate fuel enrichment for
acceleration; and a closed throttle overrun condition will prompt fuel cut-off.
The ECM provides the sensor with a 5 volt supply, and monitors the returning signal, which is proportional
to throttle opening, on an earth line.
Acceleration enrichment: When the throttle pedal is depressed, the ECM receives a rising voltage from the TP
sensor and detects a rise in manifold pressure from the MAP sensor. The ECM provides additional fuel by
increasing the normal injector pulse width and also provides a small munmer of extra pulses on rapid throttle
openings.
Over-run fuel cut-off: The ECM implements over-run fuel cut-off when the engine speed is above 2000 rpm
with engine at normal operating temperature and the throttle position sensor in the closed position, i.e. the
vehicle is coasting with the throttle released. The ECM indexes the idle air control valve open slightly to
increase the air flow through the engine to maintain a constant manifold depression and keep emissions low.
Fuel is progressively reinstated as the throttle position sensor is opened.
When using the 'Lotus Check' scanner tool, 'Throttle Bits' shows the raw signal received by the ECM from
the TP sensor, and will range from 0 (closed) to 255 (fully open). The full range of values will not be seen in
practice. 'Throttle Switch' indicates whether the ECM detects an open or closed throttle. If the display reads
'ON' when the throttle is closed, the engine will not idle correctly, and the closed throttle position may need to
be reset. Run a 'TUNE' or 'TEST' programme to reset.
To remove the sensor, unplug the harness connector and remove and discard the two Torx screws secur-
ing the sensor. Remove the clamping plate and withdraw the sensor from the throttle spindle.
To fit the sensor:
- Clean the mating faces of sensor and throttle body, and align the flat of the sensor with the machined flat
on the throttle spindle.
CAUTION: The TP sensor can be easily damaged if carelessly fitted. When pressing the sensor
onto the spindle, use only finger pressure on the centre of the sensor. Do not use the securing
screws to pull the sensor into position.
- Press the sensor into position and rotate counterclockwise to align the fixing holes.
CAUTION: Do not rotate the sensor in a clockwise direction, and ensure it is not rotated beyond
its internal stops.
- Fit the clamping plate and tighten two new Torx screws. Mate the harness connector plug.
- Operate the throttle and check that full travel of the throttle spindle, from fully closed to fully open, is
achieved.
Clamping plate
Throttle Position
(TP) sensor
Torx fixing screw
em198