Car's sitting on the drive virtually unusable. Xantia 1.8 16V 1996 I'll describe the fault and then quickly write what I've tried so far to cure it. Hopefully someone more knowledgable than I can help me, please!
One day, went out in car which had been perfect previously and found it was driving really lumpily, like timing was out or plugs were giving trouble. When I slowed down at the first junction, the revs fell to nothing and engine stalled. This happened constantly, as soon as my foot was off the pedal and speed reduced or came to a complete stop, the engine just died. Starting it up and revving wildly and keeping the engine at certain revs would sometimes keep it idling, although at erratic speeds each time, or wavering about. Sometimes it didn't work and the revs just dropped completely and engine stalled. When it started and kept idling by itself, the revs were very low indeed 500-600 rpm and a touch of the accelerator pedal caused the revs to go up a bit and then drop to nothing and stall but this would alter with each touch of the pedal. Eventually, if lucky, the car would start behaving normally when left for 5 minutes or so idling (if self-idle could be achieved by revving and messing around).
Next few days, car was fine, no more of the problem. A couple of days after that, it did the same thing again, then it was fine for a day or two. Now it does it constantly, can't really use car at all. Messing about with the revs and leaving it to idle for 5 to 10 minutes no longer creates a cure, it still stalls as soon as you try to pull off the drive and drop the revs slightly. Really lumpy too and the lumpiness changes as you mess about revving and so on, this also causes the car to stay at all sorts of different idle speeds, from 600 to 1300 rpm.
Done some work on it tonight which hasn't cured the problem but has made it far less prone to stalling - it didn't stall at all this time, despite my efforts at making it do so, but the problem is still very much there and it probably would stall when moving along under load. While messing about, I discovered the following:
- Started first time, revs went straight up to 1100 rpm.
- Pressing the accelerator a bit actually caused the revs to drop to about 500 rpm and I thought it was going to stall but the work I've done seems to help it catch itself and the revs went up a bit, to about 800 rpm.
- Revving up heavily was difficult as the revs go down first for quite a bit of the accelerator travel before going up, and they go up sporadically and won't hold, even though my foot is still they jump up to say, 3000, without moving my foot they then drop to 1500 and waver all over the place.
- Revving a tiny bit makes the revs drop and stay low and almost stall the engine. Revving up a bit more and holding it there (revs hit 1200 or so, but the pedal is much further depressed than it should be for such low revs!) I keep my foot steady but the revs go from 900 to 1200, wavering rhythmically, kind of like it would if I moved the accelerator up and down rhythmically in a normally functioning car.
- If I press the pedal to boost the revs, sometimes the revs will come down to 600 to 800 rpm and be tremendously lumpy, making the whole car vibrate. A touch on the pedal again changes the idle speed and more than likely it'll be smoother.
Now, this is what I've done so far to try and cure the fault:
- Cleaned and checked all electrical connectors that I can find, including ECU one. I have a background in electronics and did some rather bad dry joints on the ECU PCB as well.
- Have checked all vacuum hoses for leaks, cracks, etc. Everything is sound.
- Checked battery and all earth connections, everything seems in order.
- Checked air filter and pipes, all clear and clean. Can't check sparks because of the recess and lack of long adapter.
- Today removed the entire throttle housing and overhauled it and everything on it. Pipe from rocker cover to the throttle housing was partially blocked with oil residue and inside of throttle housing was covered in the thick sludge. Connecting pipe and hole through body into one venturi was completely blocked with the muck. Removed, cleaned and checked:
- Throttle potentiometer. Don't know what resistance should be.
- Throttle body heating element. Seems okay (gets hot).
- Air inlet temperature sensor. Seems okay, resistance changes with temperature (Used freezer spray).
- Idle stepper motor. End of this which acts as a valve inside the throttle housing to bypass the butterfly when closed and allow air through to the manifold was absolutely covered in a thick layer of gunge and sludge, as was the hole it acts upon inside the throttle body. Cleaned this and everything else with great care until the entire throttle body was as clean as new and all of it's associated components. Amount of sludge on the stepper motor would have impeded the air flow and action of the valve. Doing this today seems to have made it more difficult for the engine to stall, so it was a job worth doing. When the main problem is fixed, the car should idle more smoothly, etc.
Main trouble is still there though! My only thoughts now center on the MAP sensor which I haven't looked at yet cos I have to remove the entire inlet manifold to get to it. Someone said this may be the problem in an old message to a person who was suffering the same trouble as I am now. The amount of black sludge which coated the inside of the throttle body and can be seen to go into the inlet manifold makes me wonder if the sensor is covered in that and making it give false readings. I don't know though, as I have no idea what the sensor looks like or how it achieves the desired function.
Is the design of the MAP sensor such that any grime and dirt fouling of it could cause problems, or is it a "closed" type that has some kind of diaphragm to read the pressure and therefore wouldn't be too bothered by dirt? I'm thinking of removing the inlet manifold tomorrow so that I can remove the MAP sensor, but what do I look for, fault-wise and how can I check it? I have a digital multimeter, should the resistance change across two pins of the sensor in response to pressure changes, does anyone know the correct resistance measurement under normal circumstances?
Any thoughts or ideas on this fault would be greatly appreciated. We have four kids here, 3 of whom go to school and now we have no car to take them in or even do shopping. Living away from the town centre means no shops nearby. Mother-in-law gave us some food for tonight...
Sorry to write so much, but I wanted to be as detailed as possible, especially since a search of the forums shows others have had this exact same problem and not being able to find the cure, have bodged it. I'd rather find the reason and do it properly.
Thanks a lot to everyone,
James [xx(]
Xantia erratic idle, stalling and more...
Moderator: RichardW
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JamesQB
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Hi Anders,
I was actually going to edit the post and remove all of the "working perfectly" after I thought about it and decided that one can never be certain of such a thing. A device can appear to be fine yet still be faulty, especially when under conditions of load (or current when electrical).
I measured the resistance of the potentiometer from one end of travel to the other. The resistance readings were stable and continuous. If I remember rightly, it was about 90 Kilohm at the start of travel and 220 Kilohm or so at the end of the travel. The arm is obviously correctly sweeping the carbon track inside, and the results are static. I did my best to clean it inside as well, but it's almost impossible since it's glued shut.
I kept returning the potentiometer to its starting position which it should be in when the throttle isn't touched presumably (engine idling) and each and every time the resistance measurement was the same. Of course, I know the difficulty in testing these things, because they can read okay but still have flat spots. For instance, repairing a hi-fi with terrible crackling when moving the volume control (linear potentiometer) is obviously caused by the pot., but when testing it out of circuit, it reads just as it should do, because you don't detect the tiny faults on the carbon track that represent slight crackles on the sound when they're passed.
Not only that, but I don't know if the readings should be 90Kohm at starting position and 220Kohm at the end of the track! It's an assumption, perhaps the readings are far too high. All potentiometers I've come across read 0 ohms (dead short) at the start of the track and then increase in resistance upto any level they've been designed to. Maybe this one is different, it is purpose-built after all, but still, the measurements may be too high, perhaps the track has worn down and made the resistance increase? Any idea what the readings should be?
What would you recommend, purchase another throttle pot?
Incidently, the stepper motor had gunge going into it that I couldn't really access. If the movement of the motor was sometimes impaired completely, sometimes moving slightly, etc, would you expect it to cause these symptoms? I should have connected it to a power source while I had it out and made sure it was moving smoothly and consistently...
Thanks,
James
I was actually going to edit the post and remove all of the "working perfectly" after I thought about it and decided that one can never be certain of such a thing. A device can appear to be fine yet still be faulty, especially when under conditions of load (or current when electrical).
I measured the resistance of the potentiometer from one end of travel to the other. The resistance readings were stable and continuous. If I remember rightly, it was about 90 Kilohm at the start of travel and 220 Kilohm or so at the end of the travel. The arm is obviously correctly sweeping the carbon track inside, and the results are static. I did my best to clean it inside as well, but it's almost impossible since it's glued shut.
I kept returning the potentiometer to its starting position which it should be in when the throttle isn't touched presumably (engine idling) and each and every time the resistance measurement was the same. Of course, I know the difficulty in testing these things, because they can read okay but still have flat spots. For instance, repairing a hi-fi with terrible crackling when moving the volume control (linear potentiometer) is obviously caused by the pot., but when testing it out of circuit, it reads just as it should do, because you don't detect the tiny faults on the carbon track that represent slight crackles on the sound when they're passed.
Not only that, but I don't know if the readings should be 90Kohm at starting position and 220Kohm at the end of the track! It's an assumption, perhaps the readings are far too high. All potentiometers I've come across read 0 ohms (dead short) at the start of the track and then increase in resistance upto any level they've been designed to. Maybe this one is different, it is purpose-built after all, but still, the measurements may be too high, perhaps the track has worn down and made the resistance increase? Any idea what the readings should be?
What would you recommend, purchase another throttle pot?
Incidently, the stepper motor had gunge going into it that I couldn't really access. If the movement of the motor was sometimes impaired completely, sometimes moving slightly, etc, would you expect it to cause these symptoms? I should have connected it to a power source while I had it out and made sure it was moving smoothly and consistently...
Thanks,
James
Yeah well -
- that's a totally different story then - I like this much better [8D]
You're right that these values does not seem alarming [;)]
- and of course you were in fact trying to find "holes" during the slide test of the pot.
There is another very annoying problem which gives the exact same indications :
Water in the fuel !
Nothing to do with a leaking fuel filler flap (but MAY be a problem) - happens now & then at some gas stations - you simple by misshap get a squirt of water with the fuel. Especially on rainy/windy days.
As water is heavier than fuel - it will allways collect in the tank well under the fuel suction pipe/filter.
Worth a try before you rush out for expensive spares.
Be carefull working on the fuel lines in the engine compartment.
- that's a totally different story then - I like this much better [8D]
You're right that these values does not seem alarming [;)]
- and of course you were in fact trying to find "holes" during the slide test of the pot.
There is another very annoying problem which gives the exact same indications :
Water in the fuel !
Nothing to do with a leaking fuel filler flap (but MAY be a problem) - happens now & then at some gas stations - you simple by misshap get a squirt of water with the fuel. Especially on rainy/windy days.
As water is heavier than fuel - it will allways collect in the tank well under the fuel suction pipe/filter.
Worth a try before you rush out for expensive spares.
Be carefull working on the fuel lines in the engine compartment.
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JamesQB
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- My Cars: Citroen Xantia 1.8 - I miss this car a lot.
- x 5
Thanks for that, I'll check for water in the fuel. Something I didn't think of.
By the way, I now have the throttle housing out, so I've once again looked at the idle speed control valve motor, as this wouldn't actuate earlier when connected to a power supply.
There are 4 pins on the motor. The two end pins are electrically connected and the two middle pins are electrically connected but both pairs are isolated from each other. I'm using a better 12V power supply this time and trying it on each pair of contacts.
It vibrates and the valve twitches a tiny bit, but it certainly doesn't move in and out at all, no matter how I apply the voltage (to one pair at a time or both pairs simulataneously). Any idea what the 4 pins are for, I don't see why it has 4.
Just wondering if this is faulty?
Thanks,
James
By the way, I now have the throttle housing out, so I've once again looked at the idle speed control valve motor, as this wouldn't actuate earlier when connected to a power supply.
There are 4 pins on the motor. The two end pins are electrically connected and the two middle pins are electrically connected but both pairs are isolated from each other. I'm using a better 12V power supply this time and trying it on each pair of contacts.
It vibrates and the valve twitches a tiny bit, but it certainly doesn't move in and out at all, no matter how I apply the voltage (to one pair at a time or both pairs simulataneously). Any idea what the 4 pins are for, I don't see why it has 4.
Just wondering if this is faulty?
Thanks,
James
my guess would be the stepper motor.i wouldnt advise supplying the motor with power,its not really a good way to test it,the wires go direct to the ECU so im not sure how exactly its controlled but i think its by an OCR.
By the way when you took it out to clean it did you move the plunger in or out ? this is a big no no,it will damage it.
By the way when you took it out to clean it did you move the plunger in or out ? this is a big no no,it will damage it.
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JamesQB
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- x 5
I'm not testing it while it's in the car. I've got it completely removed and the little motor sitting on my bench.
Didn't move the plunger at all, doesn't seem to move. From my experience with a different type of idle motor, there was a worm drive moving the plunger and that worm drive was driven by a small motor. That design meant that the plunger couldn't be moved in or out by physical force exerting on the plunger itself. That has a bonus in so far as the plunger remains stationary when not powered rather than moving about, especially if the plunger is pressed hard against something or has a sprung-action part pressing against it.
Don't know if this motor is the same. Looking at it, I'd imagine that the four wires are present in order to supply voltage down one pair to move the plunger out, and voltage down the other pair to move the plunger in, rather than switching the voltage polarity in just two wires.
Didn't move the plunger at all, doesn't seem to move. From my experience with a different type of idle motor, there was a worm drive moving the plunger and that worm drive was driven by a small motor. That design meant that the plunger couldn't be moved in or out by physical force exerting on the plunger itself. That has a bonus in so far as the plunger remains stationary when not powered rather than moving about, especially if the plunger is pressed hard against something or has a sprung-action part pressing against it.
Don't know if this motor is the same. Looking at it, I'd imagine that the four wires are present in order to supply voltage down one pair to move the plunger out, and voltage down the other pair to move the plunger in, rather than switching the voltage polarity in just two wires.
Don't know about a bodge, but when my 1.8 16v (91K, 1995) started stalling at idle revs last year I found that there was simply far too much slack in the throttle cable where it meets the quadrant on the injector. The problem was permanently solved by adjusting the cable (yes, there's only one adjuster, a plastic plug gizmo held in place by a circlip) so that the idle revs were raised a bit.
Did I say permanent? Well yes, actually. The car's in perfect tune, doing 36-38 mpg and coping with all kinds of weather and road conditions, both in Britain and in France. Krypton test is AOK. Can't be a lot wrong with that. Have you tried tweaking the cable yet?
Mind you, if you've got gunged up pipes and all, then you won't regret having sorted those out as well.
Did I say permanent? Well yes, actually. The car's in perfect tune, doing 36-38 mpg and coping with all kinds of weather and road conditions, both in Britain and in France. Krypton test is AOK. Can't be a lot wrong with that. Have you tried tweaking the cable yet?
Mind you, if you've got gunged up pipes and all, then you won't regret having sorted those out as well.
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BonceChops
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JamesQB
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- Location: North Wales, United Kingdom
- My Cars: Citroen Xantia 1.8 - I miss this car a lot.
- x 5
I read about the cable slack and checked that but all is well. Don't know about the TDC crankcase sensor as I can't find the bugger, so much stuff above the transmission that I can't see through it all. Main problem seems to be pipes and cables, not too mention a plastic tray holding cables and pipes and God only knows what else. Is there an easy way to get to it on this car?
I got the idle stepper motor running smoothly and refitted that a short while ago. Had trouble getting it back in all the way as I'd left it with the valve too much out, so it's end was pressing hard into the airway it regulates. Trying to start the car a few times (of course, it didn't start and idle because the valve was so far out it was cutting off the idle air supply completely) and this made the plunger move in enough for me to screw the unit back in place properly.
Found it wouldn't idle at all then. Seems that the plunger valve was completely closing the airway. I couldn't help but wonder why, if the stepper motor was running fine and smoothly, the ECU wasn't detecting the lack of airflow and telling the plunger to pull in and open the valve...
Anyway, eventually got it to idle at 600 rpm by lifting the accelerator pedal until the revs were at around 350 rpm and the engine was just on the brink of stalling. Held it there for 1 minute and it suddenly jumped up to around 600 rpm (quite a lag for it to finally adjust itself and what a procedure to have to do to get it to do it?!), at this point I decided that the stepper must have moved the valve back a bit and so I gingerly removed my foot from the pedal and it remained idling at 600! With me revving a bit here and there and waiting ages, it eventually rose to around 800 rpm and stayed there. I took the beast off the driveway, noticing the revs dipping to 500 as I slowed every now and then and took it for a drive. Got back after no problems, idle was at 800 and staying there, even when moving the car, slowing, stopping, etc, no more dips to 500. Taking my foot from the accelerator caused the revs to descend nicelky to 800 and no lower and stay there.
Thing is, it's done this before without me touching anything under the bonnet and then the next day it's as bad as ever, so the fault may still be present... I think this also because it just took so much messing about and time to get it to idle after refitting the idle stepper motor, I still think it should have been much quicker at adjusting itself and getting itself to idle without stalling, surely?!
Is there a known setup procedure to go through when putting in a stepper that isn't in the same position as it was before being removed (or as in the case of putting a new unit in)? What are your thoughts on all of this?
Cheers,
James
I got the idle stepper motor running smoothly and refitted that a short while ago. Had trouble getting it back in all the way as I'd left it with the valve too much out, so it's end was pressing hard into the airway it regulates. Trying to start the car a few times (of course, it didn't start and idle because the valve was so far out it was cutting off the idle air supply completely) and this made the plunger move in enough for me to screw the unit back in place properly.
Found it wouldn't idle at all then. Seems that the plunger valve was completely closing the airway. I couldn't help but wonder why, if the stepper motor was running fine and smoothly, the ECU wasn't detecting the lack of airflow and telling the plunger to pull in and open the valve...
Anyway, eventually got it to idle at 600 rpm by lifting the accelerator pedal until the revs were at around 350 rpm and the engine was just on the brink of stalling. Held it there for 1 minute and it suddenly jumped up to around 600 rpm (quite a lag for it to finally adjust itself and what a procedure to have to do to get it to do it?!), at this point I decided that the stepper must have moved the valve back a bit and so I gingerly removed my foot from the pedal and it remained idling at 600! With me revving a bit here and there and waiting ages, it eventually rose to around 800 rpm and stayed there. I took the beast off the driveway, noticing the revs dipping to 500 as I slowed every now and then and took it for a drive. Got back after no problems, idle was at 800 and staying there, even when moving the car, slowing, stopping, etc, no more dips to 500. Taking my foot from the accelerator caused the revs to descend nicelky to 800 and no lower and stay there.
Thing is, it's done this before without me touching anything under the bonnet and then the next day it's as bad as ever, so the fault may still be present... I think this also because it just took so much messing about and time to get it to idle after refitting the idle stepper motor, I still think it should have been much quicker at adjusting itself and getting itself to idle without stalling, surely?!
Is there a known setup procedure to go through when putting in a stepper that isn't in the same position as it was before being removed (or as in the case of putting a new unit in)? What are your thoughts on all of this?
Cheers,
James
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ericthebluet
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