Secondary Air Fan; Pneumatic Switch-Over Valve; Iacv (Idle Speed Positioner); Throttle Potentiometer - Porsche Boxster Technical Manual

Boxster DME diagnosis 24
8
1. Secondary air fan
USA vehicles are equipped with a secondary air 6. Check valve
system in order to reduce pollutants in the ex-
haust gas during the warm-up phase and to fulfil
the emissions limits.
An electric air pump is mounted on the body in
the engine compartment for this purpose. It is ac-
tivated by the DME control module and, via air 7. Throttle plate part
lines, injects the secondary air behind the ex-
haust valves.
8 2. Vacuum reservoir 8. IACV (idle speed positioner)
Ensures the function of vacuum-operated compo- A two-winding positioner that is screwed directly
nents. to the throttle plate part without additional air
guide hoses.
3. Pneumatic switch-over valve
9. Throttle potentiometer
A pneumatic switch-over valve is fitted between
the air pump and exhaust valve. It is closed when The throttle position is determined via a poten-
the secondary air system is inactive and thereby tiometer fitted on the throttle-plate shaft. The
prevents the induction of additional air as a re- DME control module supplies the potentiometer
suit of flow conditions. with a controlled voltage (5 V). Depending on the
position of the potentiometer (throttle-plate
angle), there is a greater or lesser voltage drop
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across the potentiometer. The DME also recog-
4. Check valve nises the smallest opening angle of the throttle
via the voltage drop or the corresponding cur-
rent. This is defined as the "idle position".
5. Vacuum valve
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2401 DiagnosisjTroubleshooting DME 24 -D 19
Printed in Germany -4, 1996 98624D1