Uneven idle speed

ms00 · Post by **ms00** » 26 Nov 2005, 12:52

I have a Citroen Xantia 1.8 16valve injection Estate on a P plate with Magneti Marelli injection system.
The car has developed an intermittent fault with its idle speed. On start up it will not idle. After a minute or so it is fine then after ten minutes it will idle at anything between 1500-3000 rpm occasionaly "racing" (which draws concerned looks from pedestrians crossing the road!). Occasionally it will revert to a normal idle of 800 rpm.
I have checked all sensor connections which appear ok. I can only assume the idle speed stepper motor is u/s.
Having been quoted £129+VAT for a new stepper motor and none being available in local breakers, is there any way of definitively testing this part to confirm it is u/s before splashing out on a new one? Any answers gratefully recieved.

AndersDK · Post by **AndersDK** » 26 Nov 2005, 17:14

The stepper motor itself is just a stepper motor - does not contain any brains itself. All it does is obeying signals from the ECU.
You can check it by removing it and try how the motor & geartrain runs between the extremes. If its noisy and tends to stick - you need a new one.
Although named steppermotor its a perfectly nomal DC power driven device.

Otherwise I'd say its the MAP (Manifold Absolute Air Pressure) sensor fooling you (and the ECU). A common problem on all cars. I think on your Xantia model it would be a common sensor look-a-like device in the bottom of the throttle housing.

ms00 · Post by **ms00** » 27 Nov 2005, 00:33

I've had another play with the stepper motor tonight and it appears to be operating. I'll have a look at the other sensor (MAP) tomorrow, when I get the manifold off. Ta. Does anybody know what the vacuum pipe leading to a sensor in the left hand wing is? Bizarrely enough when I disconnect this the engine stops its fast idle.

Stuart McB · Post by **Stuart McB** » 27 Nov 2005, 13:33

Sounds like a classic case of oil vapour contamination of your MAP sensor. Do a site search for MAP. You'll get lots back on how to remove and how to clean. One money saving tip. If it's kaput DON'T go to you local dealer. Get the part number of the part and have a phone around some Auto electrical motor factors. You'll save pounds.

ms00 · Post by **ms00** » 28 Nov 2005, 00:00

Thanks Stuart, I have removed and cleaned the MAP sensor (which I managed without removing the manifold as Mr. Haynes suggests, woohoo!).
Unfortunately this had little or no effect and whilst I still seemed to have lost the "fast" (1500-2500 rpm) idle, I was left with no idle at all.
I turned my attention back to the idle speed stepper motor. Using my little finger as a substitute idle speed valve I managed to get a reasonable tickover. I observed the stepper motor and note that it does not move much,I can definitely feel it operating but its not moving the valve much (2mm). I have read posts about taking this unit apart but am not sure it is a wise course of action for someone who leans more to the agricultural side of mechanical engineering.
After this fiddling I refitted all and still had no tickover and joy of joys the engine management ligt came on. It being cold and starting to rain I thought well I'm blowed and disconnected the battery for a couple of minutes to brainwash the ecu and clicked the throttle cable up a couple of notches. I now have an idle speed of 1000rpm steady ish and no engine management light. Now if I could only remember the radio code.....

ps If anyone can enlighten me to the purpose of the sensor that sits at the end of the vacuum tube (which starts just below the stepper motor) behind the front left hand indicator light I would be grateful. Does this control the stepper motor?

Peter Mannn · Post by **Peter Mannn** » 01 Dec 2005, 06:50

Hi, I've been tolerating a milder form of a vaguely similar problem. So I'm very interested to see what comes of this thread. Unfortunately, I haven't much to add to what has already been disclosed. However, I suspect that carefully cleaning the wiper on the throttle potentiometer may well be worth doing, because a false throttle reading could interact with the stepper motor (I think that the stepper motor opens an idle orifice while the throttle pot is saying that the butterfly is shut). One day (when I'm not going to use the car for a few days) I' ll take the potentiometer off and see whether the case can be opened without destroying the mechanism.javascript:emoticon(':roll:')

ms00 · Post by **ms00** » 01 Dec 2005, 14:31

Hi, Peter, what you suggest sounds like a good idea. I've spent a couple of evenings playing with the car tweaking what settings are available, basically throttle, and am still legt with a car that will not idle unless the throttle cable is adjusted tight to pick the rpm up. I will have a play with the throttle potentiometer and see what happens.
Still no wiser about the mystery sensor on the passenger side wing behind the indicator.

Peter Mannn · Post by **Peter Mannn** » 02 Dec 2005, 00:58

Yes. And I believe that car manufacturers are strategically witholding this kind of information as a way of maximizing profits for themselves and their dealer networks. Makes it very difficult for do-it-yourselfers. I have been able to afford Citroens only by doing my own maintenence work, and it has been so much harder since the carburettor was replaced by anonymous electronic devices. These days I have to tolerate faults because I cannot throw money at every problem, and it has the effect of shortening the viable lifetime of a motor car.
Brings up a real sore point. The new engine management systems enable the car manufacturers to access racing technique of enriching the mixture at full throttle, so that the power statistics in the brochure look more impressive. This is why an enthusiastic right foot does horrible things to fuel consumption. In my carburettor 1974 DS, it made almost no difference : mainly because the engine works at its most efficient with throttle wide open (ie increasing compression ratio = higher efficiency) and the carby had an "honest" setup.
This is a demonstration of how the invisible hand of the market should not be trusted to manage economic and environmental factors.

ms00 · Post by **ms00** » 03 Dec 2005, 00:08

Ah, the joys of engine management systems. I spent half the day trudging around local scrapyards with the idea of obtaining a throttle assembly complete to replace the current one on the car. This I thought would narrow down the likely fault. Unfortunately all the local scrapyards only, and to me, rather surprisingly, had diesel engined Xantias. So I am in for a wait to obtain secondhand parts.
Whilst I can accept the need for engine management systems in these emmission conscious days, I find it hard to accept an engine management system that doesn't apparently recognise that the engine it is managing isn't running properly. Apart from the previously mentioned blip when the engine management light came on no fault has been indicated.
PS The radio code was sorted by producing the vehicle logbook at a citroen dealers and paying the princely sum of £15 to be told the code.

ms00 · Post by **ms00** » 11 Dec 2005, 01:26

The never ending story continues, having run out of ideas I finally caved in and took yhe motor to the garage and got it "plugged in". After a morning of checking this and that nothing obvious was found but the prime suspect is the stepper motor. So i wandered of to the Citroen dealer, ready to part with my £130, where I was helpfully informed that I could buy exactly the same part some forty pounds cheaper at the Peugot garage just down the road! Like the Citroen dealers they didn,t have one in stock but promised to have it in today. Yeah you guessed it "they forgot to put it in the delivery" and now I have to wait another three days.
Yours
getting p'd off with this

Mike

AndersDK · Post by **AndersDK** » 11 Dec 2005, 10:50

At least that was a real friendly Citroen mechanic

ms00 · Post by **ms00** » 12 Dec 2005, 23:50

Yes, Anders, a case of "I told you I'd fix the problem, I haven't, so I will not charge you". Sadly a rare quality these days, he wouldn't even take a "drink".
Still waiting for the stepper motor but have found out what that "sensor" was at the end of the vacuum pipe behind the left hand indicator light. It is the Evap switch which is where the fuel tank vents.
Mick

ms00 · Post by **ms00** » 13 Dec 2005, 19:52

I have fitted the new stepper motor and guess what... IT WORKS. Had a nailbiting few minutes when the engine was "seeking" running at between 600-1500 rpm, but I believe this was the emu learning how the new stepper motor "worked". Turned off and turned on a couple of times and now it is perfect.
Now I'm going to take the busted stepper motor apart and try and find the £100 worth of gold plating inside.

To summarise then:-
Uneven idle speed
No engine management lights
No faults recorded on emu
Cleaned all sensors/stepper motor-no effect
Therefore must be mechanical fault in stepper motor

Thanks to all for your help.
[/b]

Gregg1100 · Post by **Gregg1100** » 14 Dec 2005, 18:41

Joined: 01 Jul 2001
Posts: 134
Location: United Kingdom
Posted: Wed May 18, 2005 11:12 pm Post subject:

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Hi,
I have had bucketloads of those problems with my 16v 1998cc Xantia.
In my case it was the inlet manifold gasket blown in two places.
I changed that (without taking manifold off car ), and and all was perfect for a month or so
Car started again doing what yours is, so I nipped inlet manifold bolts up a bit and is running ok again.
Hope this helps you,
Greg

ms00 · Post by **ms00** » 15 Dec 2005, 10:55

Ah, I spoke to soon- after a couple of trips running perfectly we are now basically back to square one.
The car is once again revving at idle at between 800-1500rpm. This is cyclical i.e. you can almost here the emu saying whoops too fast and then whoops too slow this eventually settles down to minor but noticeable cycling. Then if you touch the accelerator the revs do not reduce immediately you take your foot off (Hmm. Thinks how is it getting enough air to run at 3500rpm with the throttle closed?). Once warm the engine will sporadically refuse to run or more exactly it will start, run for about 1.5 seconds and then cut out. If left for a few minutes it will start.
Yours increasingly exasperated...............

Ill try what you suggest Greg and let you all know