Xantia TD Idle Speed

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Xantia TD Idle Speed

Post by Oystercatcher » 24 Nov 2002, 04:18

For the last few days, my '98 Xantia 1.9 TD SX idle speed has been a bit fast at just over 1000 rpm. This is pretty much the speed you'd expect with the air-con on, so I wondered if there was a connection (turning the air-con on doesn't make any difference).
Anyone know how the air-con speed increase is done?. A quick look doesn't show any obvious loose connections/split hoses.

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Post by JohnD » 24 Nov 2002, 15:02

Hi Alan - Is the thermostatic sensor working OK - ie - is it releasing the fast idle lever?

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Post by Dave Burns » 24 Nov 2002, 16:25

This task is now carried out by the ECU via a vacuum pump and electrovalves, look to the right just above the rocker cover, you will see the vacuum diaphragm that controlls the idle speed, follow its pipe back to the valves, there are two valves side by side and the other one controlls the EGR.
When the engine reaches a preset temperature the ECU signals the electrovalve to allow vacuum into the diaphragm, this then pulls the cable and lowers the idle speed.
The ECU also signals the same when the speed of the cold engine is raised by the driver to a preset value, it does this because the increase in idle speed is achieved by advancing injection timing.
As you rev the cold engine you should see the diaphragm pull the cable then let go as the engine returns to idle.
Also IIRC switching on the aircon does indeed raise the idle speed by the very same method.
Check the vacuum pump on the end of the camshaft, depress the clip and pull the pipe off, it should by sucking like buggery.
Check all the pipes concerned, manually energise the electrovalve to make sure it is ok.
I'm not sure which sensor the ECU gets is temperature info from but if it has failed the ECU will assume the hot engine is still cold and keep the idle speed high.
After that you will have to look into how the aircon interacts with the system, a fault there may be telling the ECU that aircon is active when if fact its not.
Please post back with your findings.

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Post by Oystercatcher » 24 Nov 2002, 20:53

Thanks for the excellent description Dave. Now off to find a suitably shaped tuit :)

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Post by Oystercatcher » 26 Nov 2002, 04:33

Hi Dave, results so far....
I've inspected the diaphragm and valves, everything appears to be OK; all the pipework and the cable are in good condition. Revving the engine while cold does indeed move the diaphragm and fast-idle lever, so I guess the vacuum pump's working OK, but I checked it anyway - it appears to suck just fine, if not like buggery.
With the engine off, I shoved some volts up the electrovalve and could hear it moving, so I tried again with the engine running and it idled normally! - No volts = fast idle, volts = normal idle, which suggests to me that the valve, pipework, diaphragm etc. are all OK. Bugger. I guess it's a sensor (which presumably means a trip to a dealer to get the error codes read....)
On a whim I checked the voltage at the connector and saw 14v as you'd expect with a running alternator. Odd, why isn't it energising the valve? - Plugged the connector back in and the idle returned to normal. WTF!
OK, so I've disturbed something and it's now working again. If I grab a bunch of stuff and jiggle it around, what happens? - Fast idle. Ah Ha!, I've got a dodgy connection somewhere. Trouble is, no amount of fiddling restores normal idle and I'm still seeing 14v at the connector.
I'm left wondering if the valve is going open-circuit as it heats up?. The EGR valve gets warm, but the fast-idle one doesn't. I'll try again in daylight and leave it energised manually for a while to see what happens.

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Post by Oystercatcher » 19 Dec 2002, 03:05

Sorted. At last!
It _was_ the electrovalve. Tested on the bench, it would work fine for a minute or so then turn itself off. Once that happened it would refuse to work for ages.
Andy's didn't stock it, so I'm afraid it was '2nd Mortgage time'. Took a bit of tracking down too. Price? - An entirely unreasonable £28.40. Just as well they sold them singly and not as the pair c/w bracket!
Ho Hum

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Post by biomed32uk » 31 Dec 2002, 19:53

More of a question for you really, I think I have the same problem, the diaphram is sucked in on the vacuum unit after a half hour run to work but the cable seems very loose, the nipple on the fuel pump end is about 6 mm away from the fast idle arm, if i poke the end of the fast idle arm with a screwdriver the idle slows down, I would presume that at rest and cold this should all be just touching so when the engine warms up it pulls the arm on the pump over...
Would I be presuming right here and can I adjust it out at the threaded sleeve and locknut by the vacuum unit?????
Thanks for any help....

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Post by Oystercatcher » 01 Jan 2003, 03:03

Sounds like you valve is OK as the diaphragm will be 'in' with the engine running and everything up to temp. On mine, the cable is taught when that happens. IIRC there's a little bit of play in the cable when cold and the nipple is touching the fast-idle lever.
It's the only adjustment I can see, so it's worth a try <img src=icon_smile.gif border=0 align=middle>. Let's hope you haven't got a broken cable.
Happy New Year

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Post by David W » 10 Jan 2003, 21:51

Funny thing this idle speed on the '97 TDs with the vac and electrovalve arrangement.
Dad bought a used Xantia from a small dealer and returned it to them complaining about the constant high idle. The sent it to their usual small garage who said it was a Citroen only job.
He booked it into Citroen and after an hour they declared it "as good as you'll get it, it's the computer that controls these".
Eventually I got to look at it and found it had a failed electrovalve. Had some trouble describing it to the Citroen parts dept and they couldn't remember ever supplying one. As you say Oystercatcher you just get the one valve for about £30 and have to drill the fixings out to attach it to the existing assembly with the pair on one bracket.
We also found the cable from the vacuum unit was stiff so changed that as well. Perfect operation from then on.
Proving this fault was made easier with one of those vacuum tester kits with a pump and gauge.

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Post by NSP » 03 Nov 2003, 09:35

In case this is helpful; I have a Xantia with 195k on the clock. I've done the last 120k so am well versed in replacing the Electro-valves. However, My car started doing the random fast-idle again recently, and changing both the electro-valves, and even the temp sender behind the fuel filter did not remedy. Almost at point of giving up I found that disturbing the connections at the front of the injector pump had an effect. I then cleaned the blades inside the three connector blocks on the front of the pump, and applied a very thin film of very expensive copper grease to ensure a good connection. 5k down the road, and it's not mis-behaved once since! It would appear that a ropey connection in the most unlikely of places can send the ECU into a spin??