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Originally posted by G Force
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Hi Patrickingham there is one normal condition where the engine is sometimes reported as over-revving which will not be cured by the following procedures, so I think it warrants a mention. If the car is started from cold and driven for “any” distance, the engine revs will hang around 1100rpm (or slightly higher in the first 2 miles) each time the clutch is depressed to change gear, the engine revs will not return to controlled idle speed until the first time the car comes to a full stop.
If you are having problems with erratic idle speed over revving etc. with a Lucas Hot Wire fuel injection system you should reset the base idle, CO, and most importantly the throttle pot setting. You can just try set the base idle and throttle pot but for best results its best to go through the following full procedure. It looks very long-winded I know, but if you break it down into small sections it isn’t anything like as complicated as it first might seem.
I, like G51 NAV says, would normally recommend cleaning the throttle body out before you do anything as the gunk that accumulates is part of the problem. To avoid all the gunk going into the engine the best way is to remove the throttle body first, and then if you don’t have a big enough spanner you can use a vice to help unscrew the stepper motor. Give everything a good thorough clean with carb cleaner to remove all the gunk that accumulates. Clean all the deposits from all around the throttle butterfly disc and large breather port, and you will probably find the small crankcase breather port needs unblocking as it is nearly always blocked.
To set the base idle the engine needs to be hot. Then you need to ensure the stepper motor is fully closed (there is a special tool for this) but you can do it by using the following method.
Turn on the ignition and wait 10 seconds then remove the stepper motor plug, then turn off the ignition and wait 30 seconds or until you hear the main relay click out. Then replace the stepper motor plug and turn on the ignition and wait 10 seconds, and then remove the stepper motor plug again. Turn off the ignition and wait 30 seconds etc. Then repeat once more this will ensure the stepper motor is fully closed. With the stepper motor plug disconnected start the engine and set the idle speed to 650rpm with the throttle stop screw. Then replace the stepper motor plug.
After setting the base idle you will need to reset the throttle potentiometer with a voltmeter to read 325mv output with the throttle closed with ignition on. To set the throttle potentiometer you will need a suitable multi–meter and an allen key or angled pozi–drive screwdriver.
There are three wires going to the potentiometer from the fuel injection ECU The harness wires are coloured as followed: pink with black trace, pink with purple trace and a third which varies from model to model and is either green with red trace or green with yellow trace.
With the ignition switched on and the throttle potentiometer harness connected push the probe of the black wire of the multi – meter into the pink and black wire of the vehicle harness throttle potentiometer connector. Then push the probe of the red with of the multi–meter into the green and red wire of the vehicle harness throttle potentiometer connector. If your harness has a different colour wire always remember that the pink and purple wire is never connected into with the meter.
With the multi – meter set to the mv setting measure the voltage reading. The reading should be 325mv +/-10mv with the throttle fully closed. If the reading is incorrect then the two screws holding the throttle potentiometer to the throttle body can be loosened enough to move the potentiometer to obtain the correct reading. Take care as when the screws are re tightened the setting can alter. Open and close the throttle butterfly a few times to ensure the reading stays constant when the butterfly is closed. I find that sometimes it is easier not to loosen the screws of the potentiometer and just tap the potentiometer body gently with the handle of a screwdriver to obtain the correct reading, obviously sometimes loosening the screws is the only option if more force would be needed.
Once you have done this with engine at normal temperature set the CO to 2% with the screw on the throttle body nearest the stepper motor, that’s if you have access to a gas analyser of course. The mixture screw is on the throttle body just in front of the stepper motor. It is an air bleed and only affects idle mixture so don’t expect it to make a big difference to performance. To richen the mixture you will need to turn the screw clockwise, it will probably take a full turn to take the CO setting from 0.75 up to the 2.5 max.
If the engine stalls when coming to a halt it could be a faulty road speed transducer. To test the transducer disconnect the harness plug and connect a multi-meter set to read Ohm’s across the transducer wires. Then jack up one wheel and rotate the wheel observing the reading on the meter, it should fluctuate between 0 Ohm’s & open circuit.
Regards Gary
If you are having problems with erratic idle speed over revving etc. with a Lucas Hot Wire fuel injection system you should reset the base idle, CO, and most importantly the throttle pot setting. You can just try set the base idle and throttle pot but for best results its best to go through the following full procedure. It looks very long-winded I know, but if you break it down into small sections it isn’t anything like as complicated as it first might seem.
I, like G51 NAV says, would normally recommend cleaning the throttle body out before you do anything as the gunk that accumulates is part of the problem. To avoid all the gunk going into the engine the best way is to remove the throttle body first, and then if you don’t have a big enough spanner you can use a vice to help unscrew the stepper motor. Give everything a good thorough clean with carb cleaner to remove all the gunk that accumulates. Clean all the deposits from all around the throttle butterfly disc and large breather port, and you will probably find the small crankcase breather port needs unblocking as it is nearly always blocked.
To set the base idle the engine needs to be hot. Then you need to ensure the stepper motor is fully closed (there is a special tool for this) but you can do it by using the following method.
Turn on the ignition and wait 10 seconds then remove the stepper motor plug, then turn off the ignition and wait 30 seconds or until you hear the main relay click out. Then replace the stepper motor plug and turn on the ignition and wait 10 seconds, and then remove the stepper motor plug again. Turn off the ignition and wait 30 seconds etc. Then repeat once more this will ensure the stepper motor is fully closed. With the stepper motor plug disconnected start the engine and set the idle speed to 650rpm with the throttle stop screw. Then replace the stepper motor plug.
After setting the base idle you will need to reset the throttle potentiometer with a voltmeter to read 325mv output with the throttle closed with ignition on. To set the throttle potentiometer you will need a suitable multi–meter and an allen key or angled pozi–drive screwdriver.
There are three wires going to the potentiometer from the fuel injection ECU The harness wires are coloured as followed: pink with black trace, pink with purple trace and a third which varies from model to model and is either green with red trace or green with yellow trace.
With the ignition switched on and the throttle potentiometer harness connected push the probe of the black wire of the multi – meter into the pink and black wire of the vehicle harness throttle potentiometer connector. Then push the probe of the red with of the multi–meter into the green and red wire of the vehicle harness throttle potentiometer connector. If your harness has a different colour wire always remember that the pink and purple wire is never connected into with the meter.
With the multi – meter set to the mv setting measure the voltage reading. The reading should be 325mv +/-10mv with the throttle fully closed. If the reading is incorrect then the two screws holding the throttle potentiometer to the throttle body can be loosened enough to move the potentiometer to obtain the correct reading. Take care as when the screws are re tightened the setting can alter. Open and close the throttle butterfly a few times to ensure the reading stays constant when the butterfly is closed. I find that sometimes it is easier not to loosen the screws of the potentiometer and just tap the potentiometer body gently with the handle of a screwdriver to obtain the correct reading, obviously sometimes loosening the screws is the only option if more force would be needed.
Once you have done this with engine at normal temperature set the CO to 2% with the screw on the throttle body nearest the stepper motor, that’s if you have access to a gas analyser of course. The mixture screw is on the throttle body just in front of the stepper motor. It is an air bleed and only affects idle mixture so don’t expect it to make a big difference to performance. To richen the mixture you will need to turn the screw clockwise, it will probably take a full turn to take the CO setting from 0.75 up to the 2.5 max.
If the engine stalls when coming to a halt it could be a faulty road speed transducer. To test the transducer disconnect the harness plug and connect a multi-meter set to read Ohm’s across the transducer wires. Then jack up one wheel and rotate the wheel observing the reading on the meter, it should fluctuate between 0 Ohm’s & open circuit.
Regards Gary
many thanks for the brilliant advice gary, you know your stuff
Haven't given up though 
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