Xantia THROTTLE POTENTIOMETER AND STEPPER MOTOR
I've noticed some traffic recently on the subject of a throttle potentiometer and a stepper motor. On reflection, it could explain the abberations that my engine sometimes displays if it were the case that the potentiometer was flaky and the stepper motor was struggling to do its task due to failure of lubrication.
In thinking that, I've presumed that the potentiometer indicates throttle angle to the ECU, and that the steppermotor controls the rate of throttle closure.
Can somebody confirm, or furnish the correct roles for these electronic beasties that dwell below the intake throttle.
Incidentally, provided that the track is OK, cleaning the wiper contact will often restore proper function to a potentiometer. Be careful not to bend its little arm too
far.
Xantia THROTTLE POTENTIOMETER AND STEPPER MOTOR
Moderator: RichardW
You are correct about potentiometer.
About idle stepper motor, you are quite close. On most engines (including those on Xantia), idle stepper motor controls opening of additional air passage when throttle butterfly valve is closed. Throttle valve closes immediately and fully when you move your foot from the pedal.
About idle stepper motor, you are quite close. On most engines (including those on Xantia), idle stepper motor controls opening of additional air passage when throttle butterfly valve is closed. Throttle valve closes immediately and fully when you move your foot from the pedal.
Thanks for your reply Alexx.
My 2 litre injected 1994 Xantia ( 50,000 miles) has a throttle response unlike any older Citroen that I have driven, in that the engine revs are a lot slower to rise after application of throttle. This slow throttle response not uncommonly catches me out on stationary starts, with the engine stalling as the clutch engages while the motor dithers and mumbles.
Another curious difference is that the engine revs decrease much more slowly when releasing the throttle (as in gear changes).
I understand that some damping of engine response can contribute to overall smoothness when adjusting throttle to shed or add speed, but this seems excessive, and makes for a slow gearchanges when matching engine and gearbox speeds to shift gears (reduces wear of the clutch friction material).
Is this attributable to a fault in stepper motor function ?
My 2 litre injected 1994 Xantia ( 50,000 miles) has a throttle response unlike any older Citroen that I have driven, in that the engine revs are a lot slower to rise after application of throttle. This slow throttle response not uncommonly catches me out on stationary starts, with the engine stalling as the clutch engages while the motor dithers and mumbles.
Another curious difference is that the engine revs decrease much more slowly when releasing the throttle (as in gear changes).
I understand that some damping of engine response can contribute to overall smoothness when adjusting throttle to shed or add speed, but this seems excessive, and makes for a slow gearchanges when matching engine and gearbox speeds to shift gears (reduces wear of the clutch friction material).
Is this attributable to a fault in stepper motor function ?
Well, my 1.8 16v Xantia ('98, 49.000 km) also behaves differently than BX.
Upon releasing throttle at about 3000 min-1, engine maintains the same revs about a second, then within next 2 seconds they gradually drop to idle. But, this process is smooth and idle is perfectly stable, there are no other problems with engine - it seems to be in perfect condition (like the rest of the car).
Before buying this car about a month ago, I tested several new cars, and some of them - Ford Focus (1.6 16v) and Renault Laguna (1.8 16v) behaved in a very similar fashion, so I presume this behaviour is 'normal'. In the meantime, I get used to it - before the gearchange, first release the throttle and than press the clutch - gearchange is very smooth that way, although not very fast.
Obviously, this is controlled with the stepper motor. When you release the throttle and press the clutch, it opens, than gradually closes (not completly, of course). I also noticed another thing - if you let the revs drop under 1500 with the throttle released and clutch engaged, engine gradually starts to 'push the throttle', preventing it form stalling, obviously also with the idle motor.
After application of the throttle, revs rise about twice slower than in BX, but this shouldn't be connected with the stepper motor, because throttle valve is open in that case - I think ECU is programmed this way. So, it's necessary to press the throttle before start releasing the clutch and not in the same time like in BX.
Once you get used to this, gearchange is very smooth, but I didn't like this at first.
Maybe someone else can tell us about his car's behaviour ?
Upon releasing throttle at about 3000 min-1, engine maintains the same revs about a second, then within next 2 seconds they gradually drop to idle. But, this process is smooth and idle is perfectly stable, there are no other problems with engine - it seems to be in perfect condition (like the rest of the car).
Before buying this car about a month ago, I tested several new cars, and some of them - Ford Focus (1.6 16v) and Renault Laguna (1.8 16v) behaved in a very similar fashion, so I presume this behaviour is 'normal'. In the meantime, I get used to it - before the gearchange, first release the throttle and than press the clutch - gearchange is very smooth that way, although not very fast.
Obviously, this is controlled with the stepper motor. When you release the throttle and press the clutch, it opens, than gradually closes (not completly, of course). I also noticed another thing - if you let the revs drop under 1500 with the throttle released and clutch engaged, engine gradually starts to 'push the throttle', preventing it form stalling, obviously also with the idle motor.
After application of the throttle, revs rise about twice slower than in BX, but this shouldn't be connected with the stepper motor, because throttle valve is open in that case - I think ECU is programmed this way. So, it's necessary to press the throttle before start releasing the clutch and not in the same time like in BX.
Once you get used to this, gearchange is very smooth, but I didn't like this at first.
Maybe someone else can tell us about his car's behaviour ?
I can confirm the general behaviour of the Xantia 2.0 engine - mine is similar ( in the brief periods that it actually makes it onto the roads[}:)] ). The motors can get dirty and lose some of their effectiveness, so maybe if the response is excessively slow it might be worth cleaning it. I've had a few of these pesky things out recently from our cars, and in every case, a good clean worked wonders. I've had the one from the Xantia out twice, because the engine kept stalling when the throttle was closed. I've sorted it now though!
Stu.
Stu.