OMEM710 Hardware Manual 2v11
36
The Idle Fuel table is required for engines that are using air bypass with throttle position as the
main load sensor. On TPS load based engines, the load sensor (the TPS) does not measure the
extra air flow due to the opening of the idle motor, so does not compensate with extra fuel in the
main fuel map to maintain the target lambda (air/fuel ratio). An oxygen sensor cannot make
adjustments to the fuelling fast enough to cope with these changes. This table allows a fuel trim
based on idle motor duty to maintain a constant lambda value. This is not required for MAP based
systems so would be set to 0 in this case.
Testing correct operation of a 2 wire idle motor
Remove the idle motor from the engine.
Ensure that the idle motor has a constant power supply. If powered from a relay controlled by
the ECU you will need to temporarily ‘bridge across’ this relay to give the idle motor constant
power.
In the Idle Duty Coolant Table find the current engine temperature and set that site and the
sites either side to 0 which should close the valve. Set the sites to 100 and the valve should
move to fully open. Some idle motors (usually Bosch parts) are slightly open when at a value of
0, then close at about 30, then start to open again until fully open at 100. The value at the
closed position must be inputted to Idle Duty Min.
Testing correct operation of a 3 wire idle motor
Remove the idle motor from the engine.
Ensure that the idle motor has a constant power supply. If powered from a relay controlled by
the ECU you will need to temporarily ‘bridge across’ this relay to give the idle motor constant
power.
In the Idle Duty Coolant Table find the current engine temperature and set that site and the
sites either side to 0 which should close the valve. Set the sites to 100 and the valve should
move to fully open. If the opposite happens i.e. the valve is fully open at a value of 0 then either
swap the 2 IDLE wires at the idle motor connector or swap the Idle PWM1 out and the Idle
PWM2 out.
Some idle motors (usually Bosch parts) are slightly open when at a value of 0, then close at
about 30, then start to open again until fully open at 100. The value at the closed position must
be inputted to Idle Duty Min.
Testing correct operation of a 4 wire stepper motor
Turn ignition off.
Remove the stepper motor from the engine.
Hold the stepper motor with the plunger facing very close (approximately 5mm) to a hard object.
Ignition on. The stepper motor’s plunger should push outwards for approximately 1 second then
retract slightly. As it pushes out you must resist this by pushing it against a hard surface else the
plunger can fall off.
If the opposite happened i.e. the plunger retracted for a second, then pushed outwards slightly,
either swap the IDLE1 and IDLE2 wires at the stepper motor or swap the setting of Idle1
Stepper Out and Idle2 Stepper Out.
Setting air bypass idle control on MAP for load engines
As the idle motor opens and closes, the manifold pressure changes and so the position on the main
fuel maps moves, meaning the fuel requirement changes will be compensated for by the main fuel
map. Therefore, ensure that the Idle Fuel table is set to 0 throughout. Ensure that all Fuel Map
sites around idle (including those towards stall) are correctly calibrated before attempting this setup
for the final time.
Turn the scatter spark control and motor feedback control off by setting Idle on below RPM to
100rpm so that the engine will not enter the idle condition.
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