Uneven idle speed

Gregg1100 · Post by **Gregg1100** » 15 Dec 2005, 20:23

Hi,
Try squirting some WD40 around inlet manifold edges first. If engine note changes, it is sucking in air and gasket is shot..
I bought a potentiometer, and a stepper motor - both nothing wrong with the old ones--before the manifold leaks were found. The MAP sensor on my 16v, 2 litre, just looks like an oil pressure switch, with no moving parts. Local Citroen garage has never sold a MAP sensor, in their stores or anywhere in Wales.
I sometimes get the jerking and revving still, but just take off all the pipes from the rocker box at top, clean them out with carb cleaner, clean out the stepper motor housing( after removing stepper motor and potentiometer ). This stops the revving/jerking at once. I have got to get around to putting a petrol filter in the breather pipeline, then this will be stopped altogether.
Hope this helps
Greg

ms00 · Post by **ms00** » 15 Dec 2005, 23:39

Thanks for that Greg, I will try all your suggestions on Saturday (work comitments etc) and let you know how I get on. Funnily enough I drove the car today and it behaved itself apart from a slightly erratic idle speed once driven 8 miles or so.

ms00 · Post by **ms00** » 14 Jan 2006, 22:03

Apologies for the abscence, Christmas and an exploding starter motor on the Volkswagen skip have got in the way not to mention the complete abscence of scrapping petrol Xantias down here in Dorset.

Tried the WD40 stuff to no avail, took car to another Citroen specialist who said he'd "never seen a Xantia do that before!"; You can imagine my joy at hearing that.

Finally tracked down a Xantia in an (almost) local scrapyard. The guy running the place was most helpful and helped me do a series of tests replacing various sensors/ throtle body / emu etc.

Finally found the culprit...............it was the MAP sensor. This despite the original testing OK and not being picked up on as a fault by the emu. As soon as I put the new (to me) MAP in all symptoms disappeared.

Many thanks to all of you for your useful suggestions and especial thanks to www.pilsdonautos.co.uk for being extremely helpful.

Mick

Mandrake · Post by **Mandrake** » 15 Jan 2006, 02:13

When your MAP sensor was faulty did you notice any problems with lack of performance or excessive fuel consumption ?

My 2.0i also intermitantly idles between 800-1100rpm, and I also notice (compared to my Dad's Xantia with identical engine) that the performance isn't as good as it used to be, and I also struggle to get any more than 10Km/litre regardless of how I drive.

Still not sure where the MAP sensor is on a 2 litre 8 valve petrol though - havn't seen any pictures of it... and trying to follow peoples anecdotal descriptions of what it looks like and where it is just leaves me scratching my head..

Regards,
Simon

ms00 · Post by **ms00** » 15 Jan 2006, 12:42

Hi Simon,

No, there was no particular increase in fuel consumption or lack of performance noticeable, in fact at over 2000 rpm the car ran smoothly and normally. The major symptoms were the up and down (cycling) idling speed and poor starting when hot.

My MAP sensor (and the 2Li 16valve) is on the inner side of the plastic inlet manifold. It is secured by a single 10mm bolt. Not certain about the 8 valve engine but I think it is remotely mounted on the right hand wheel arch at the end of a vacuum tube. It will have a wiring plug going into it as well.

If it is mounted on the inlet manifold like mine you will probably have to remove the throttle body and air cleaner to get (restricted) access.

The one on my car looks like a 5x2 cm black plastic block with an angled plug connector and a 1cm hollow stub with a rubber grommet which plugs into the manifold.

Gregg1100 · Post by **Gregg1100** » 15 Jan 2006, 14:05

Hi,
My MAP sensor doesn`t sound like the description that you gave of yours. When I was checking out all the gubbins that may have been giving me the aggro, I was told by Citroen main dealers that they had never sold a Map Sensor, nether had anyone else in Wales. My car is a 1997 VSX 2 litre 16v, and the MAP Sensor for that, looks just like an oil pressure switch, - probably just measures manifold pressure/ depression. Glad you got it sorted out. Pic of my Map Sensor is below:

http://img.photobucket.com/albums/v676/ ... SENSOR.jpg

Regards,
Greg

Mandrake · Post by **Mandrake** » 16 Jan 2006, 08:10

ms00 wrote: My MAP sensor (and the 2Li 16valve) is on the inner side of the plastic inlet manifold. It is secured by a single 10mm bolt. Not certain about the 8 valve engine but I think it is remotely mounted on the right hand wheel arch at the end of a vacuum tube. It will have a wiring plug going into it as well.

Yep, that seems to be it. It's mounted near the right wheel arch with a long hose to the inlet manifold. If I pull the hose off it while the engine is running, the idle speed drops very slow to the point of stalling, while on the other hand if I disconnect the other vaccum hose to the manifold (going to some kind of dashpot ?) then the idle speed rises a lot if that port is left unblocked, but idles normally if I put my finger over it.

Could the slighly high idle speed just be an intermitant air leak on the inlet manifold, not necessarily the sensor itself ?

Regards,
Simon

ms00 · Post by **ms00** » 17 Jan 2006, 23:46

Hi Greg,
Mine is completely different to that. As described an all plastic construction.
Hi Simon,
Glad you found it, The other hose I think goes to the evap thingymajig which vents the fuel tank. Does the vacuum hose go to the manifold or the throttle body? As for the intermittent air leak, try Greg's WD40 trick mentioned previously.

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