300Tdi Discovery
19
FUEL SYSTEM
2
FAULT DIAGNOSIS
BASE IDLE SPEED SETTING
NOTE: Base idle speed is set at factory. It
should not require further adjustment
unless plenum chamber is changed. The
adjustment screw is sealed with a plug to prevent
unauthorised alteration. Check ignition timing
before attempting following procedure, since this
will affect idle speed.
Equipment required
Two blanking hoses. these are manufactured using
a new air by-pass valve hose - Part No.ETC7874. Cut
two equal pieces 90mm long from hose and seal one
end of each, using 13mm diameter bar. Use a suitable
clamp to ensure an air tight seal.
Checking procedure
1. Drive vehicle at least two miles until engine and
transmission are hot. Switch off engine.
2. Check all electrical loads are OFF, including air
conditioning.
3. Remove air by-pass valve hose.
4. Fit blanking hoses to both plenum chamber and
air by-pass valve. Ensure hoses are securely
fitted to prevent air leaks. Note throttle cable and
cruise control actuator have been omitted from
illustration.
5. Start engine and check idle speed is within
limits.
See ENGINE TUNING DATA,
Information, Engine 3.9 v8i
Adjusting base idle speed
6. Drill tamper proof plug and insert a self tapping
screw to enable plug to be extracted.
7. Start engine, adjust idle screw clockwise to
decrease or counter-clockwise to increase idle
speed.
8. Stop engine, remove blanking hoses. Reconnect
hose to plenum.
9. Fit new tamper proof plug.
