Base Idle Speed Adjustment

Rover 800 and 820  models with Lucas Hot wire Efi


 


Early Rover 820I, 820Si models use Lucas "Hotwire" Multipoint Efi, the means of adjusting the base idle speed varies according to the type of throttlebody fitted. Only one type is shown in the Haynes manual for the 800 although details of the other type are given in the Haynes manual for the Montego 2litre Efi.

Throttlebody Types:

Type (A) has an external stop screw acting directly on the throttle butterfly spindle adjacent to the throttle cable fixture – this is the type shown in the Haynes manual.

Type (B) has an adjusting screw regulating the flow through a butterfly by-pass passage. This located on the same side as the idle mixture adjustment screw but are about 30mm towards the front of the throttlebody and about 10mm lower down. An alloy plug to discourage tampering might seal both this and the mixture adjustment screw, this can be easily hooked out with a pointed tool such as an awl. Note removal of these seals is not permitted by law in some countries except by Rover dealers
 
 

Preparation

Before attempting any adjustment check the connections to the water temperature sensors and the fuel temperature sensors are in good order, also check the little rubber vacuum pipe to the Ignition system ECU is clear and in good order, likewise the airfilter should be clean. Also check for vacum leaks, ignition faults such as a trcking distributer cap or a deffective plug lead..

Assuming the rest of the engine is in good order now get the car fully warmed up, to ensure with the engine idling the electric fan should be allowed cut in and cut out again.

Check the voltage of the throttle position sensor sometimes called the TPS it is a simple carbon track potentiometer  and is located on the opposite side of the throttlebody to the accelerator cable. it should read 0.325 volts  plus or minus  0.025 volts between earth and the centre connection.
This can be adjusted by slackening the two Torx fasteners, which locate it on the throttlebody.
Also check it operates smoothly, giving an even and repeatable voltage change in response to opening and closing the throttle.

For all electrical checks on car electronic systems it is advisable to use a digital multimeter not an analogue type as the analogue type draw a higher current which may either damage a circuit or give a false low reading.

If you have suitable an instrument such as a "Gunson Gastester" to measure the CO content of the exhaust gas check that the CO emission are 1% (+ or –0.5% ) for non catalyst equipped cars in practice 1.5% is a good target for a high milage car of this type. Catalyst equipped cars should return a exhaust CO reading of less than 0.5%

Cycling the Stepper Motor

The next stage is to cycle the idle speed stepper motor to the base idle position.

(1) Switch on the ignition
(2) Count to 10
(3) Disconnect the electrical connection to stepper motor (the black "spark plug like" object on top of the throttlebody). (4) Switch off the ignition
(5) Count to 10
(6) Reconnect the stepper motor

Repeat steps 1 to 6 once more

Then repeat steps 1 to 4
 

DO NOT RECONNECT THE STEPPER MOTOR AT THIS STAGE

The stepper motor should now be in the base idle position i.e. fully extended and the by-pass valve will be fully closed.

Now start the car and adjust the base idle speed to 750 RPM plus or minus 25 RPM for manual transmission cars and 725 RPM for automatics.

Note:
If you have a "Type (A)" throttlebody turning the stop screw clockwise increases the idle speed.
If you have a "Type (B)" throttlebody turning the volume screw anti-clockwise increases the idle speed.

Switch off the ignition and reconnect the Stepper motor and start the engine. The idle speed with the ECU controlling the stepper motor should settle at 900 plus or minus 50 RPM but may rise above this at times.

Check the voltage output from the throttle position sensor and adjust again if required.

Check the CO content of the exhaust gases again, if it falls outside the specified limits reset the idle mixture and repeat procedure for setting the base idle speed.

If after carrying out this procedure the idle speed is still unsatisfactory try the following.

(1) Cleaning out the throttlebody and the small bore pipe to the airfilter.

(2) Clean and lubricate the stepper motor with "WD40" or "Redex"

(3) Check the resistance of temperature sensors.

(4) Check thermostat is operating at the correct temperature.

(5) Check for an ignition fault.

(6) Carry out a compression and/or cylinder leakdown test.
 

(Note this procedure does not apply to 820e and 820Se models fitted with single point injection or to cars fitted with the later Rover MEMS Efi.)
 

Andrew W. MacFadyen B.Eng.Hon(Mechanical)

3/2/1999

Return to Contents Page