Idle speed hunting

[CFO]

Over the last couple of days my '96 2.0 litre Xantia auto began to need a bit more winding to start. It then began to stall on idle although if I reduced the throttle very gently it would sometimes stay in. Switching off the aircon helped by reducing the load at idle. I have had this problem once before and had a spare Magneti Marelli idle speed solenoid on the garage shelf. I tried this but the idle speed now hunted between 1500 and 2000rpm. Going back to the original solenoid valve, that now hunts as well, and driving it for a few miles hasn't tuned it in. I have a feeling that we have disturbed a setting somewhere, but can't think how. Any suggestions, please?

[RichardW]

My Dad's 1.8 did similar just before the crank sensor karked it.....

[Mandrake]

You don't say whether the car drives ok above idle - does it accelerate normally on the throttle or are you lacking power there too ? Is the engine management light on ? (I'm guessing not) Does it have a vibration and lack of power that you would expect from a misfire ?

An unstable idle and difficult starting could be many things - MAP sensor, TPS, coolant temperature sensor, (if it only happens on a cold engine) idle control valve (but only if the power is normal with the throttle open) etc...

To get some direction it would be best to get it read on a Lexia - see if there is a forum member near you with a Lexia.

Otherwise you could waste quite a bit of time and money with shotgun diagnostics (parts changing) and still not solve it.

That's a good engine, I had one the same as yours for four years and the engine was completely trouble free, and apart from oil, filters and timing belt I never needed to do any work to the engine in the 20k miles I did in the car...

[CFO]

Hi Mandrake - many thx for coming back on this. The car drives absolutely fine above idle, although on light throttle, I can feel the hunting coming through. Management light is not on, and we have checked the pipe from the manifold throttle body to the IMAP sensor - that's clear.

What puzzles me most at the mo is that originally, the engine ran smoothly, but the idle speed seemed a little too low to keep it running when I took my foot off at a junction or roundabout. But now, after taking off the MM idle speed valve and cleaning it up (pretty oily and gungy) it has gone over to this higher speed hunting behaviour. That's the only part we have touched, which is why I am inclined to concentrate on it. Have just spent an hour searching the net, and altho' there is lots about Harleys and other bikes, there's nothing helpful about Cits.

Does anyone maintain a list of Lexia owners? We are in S Oxfordshire

[myglaren]

There is a list and map here.

[handyman]

If, as you say, the idle speed motor was all gungy when you took it out, chances are the chambers that utilize this control are also in a similar state.

The remedy is to take off the throttle body, strip out all the electrics and give the remains a thorough cleaning, paying attention to the small bypass chambers, as these do get clogged up with oily residues. Once cleaned, refit all the gizmos, bolt back into the car & you'll have eleminated that problem. Its also worth checking all the small pipes that feed into the unit for blockages.

Then its time to stick the Lexia on & test.

If your car is one of the XU engines with the later plastic throttle bodies, its also worth checking the spindle on the butterfly flap, as these can wear considerably, especially on higher mileage engines, allowing air to be sucked into the inlet, thus upsetting the idle mixture. Best cure is to fit one of the older alloy bodies, if you can find one.

Shame you not nearer to me as I've cured a few of these problems on XU engined Xantias.

Other things worth checking are leaking gaskets between the inlet manifold & head, spark plugs & ignition pack, especially the insulated connector sleeve between plug top & coil outlet. Are all your plugs fitted tightly into the head?

H

[CFO]

Hi H - thx for coming back on this. I am very hopeful that we have solved it. Following lots of advice, we took off the throttle body and gave it a thorough clean. On reassembly and starting up, it hunted just as badly as before - BAD NEWS! However, the GOOD NEWS is that we decided as a last resort to disconnect the battery and force all the systems to restart. That cured it - started up sweet as a nut and settled down to a smooth tickover at 800rpm. A quick test drive suggests that it's AOK - fingers crossed.

[citronut]

as i said over on the CCC forum

"my experience of the idle stepper motor is,

on giving them a good blast of carb cleaner with it off the car, then re/fitting it they run ok for a short while, then revert back to fluctuating idle speed,

till i discovered after cleaning with carb cleaner this leaves the completely dry inside, so a shot of a very light oil like Three in one or duck oil,

this gets them working as they should, as they usually fail in the first place through getting jammed up with carbon build up,

maybe the one you had on the shelf was just sticking from laying around,


do not use that orible W stuff in the attempt to lubricate them, as its NOT a lubricant,

the way to re/calibrate these after re/fitting is switch the ignition on and off 2 to 3 times,"

[Mandrake]

Interesting you should say that Malcolm, I have idle speed hunting problems on my V6 - it will idle steady if left alone but its reaction to changing conditions is poor like its overshooting the desired target speed.

For example after revving the engine the idle speed will drop below normal trying to stall then surge higher before recovering.

When I cleaned it out with carb clean (it wasn't that dirty) it actually got worse not better, and it felt to me that the bearing was a bit "loose" and too easy to turn - it would spin wildly back and forth if I spun the housing in my hand.

Perhaps squirting some oil into the bearing gives it a little bit of fluid drag/damping that it needs to damp its reaction to the command from the computer ?

If I hadn't already given up on this car I would whip the idle control valve out and give the bearings a squirt of oil as you suggest...(although its very hard to target the bearings on this design without it going everywhere)

I agree that the second hand one that the OP fitted which gave a 1500rpm idle speed was probably just stuck open.

[handyman]

When taking off or refitting the idle stepper motor, you MUST first disconnect the battery. This stops the unit being energised until you turn on the ignition & the ECU can then reset the parameters for the motor.

It is advisable not to go poking around or pulling/pushing the piston, as the circuitry that controls the motor is quite delicate. For cleaning, get some electrical switch cleaner as this will clean any dirty internal contacts, without leaving a residue & lubricate the internals. If you own a Citroen, its obligatory to keep a tin if switch cleaner.

H

[addo]

I've pulled the pintle right out, washed in the parts cleaner and reassembled with new grease. Still runs like a bought one.

First thing I'd be having the OP check is battery terminals and current stability. At this age, it's highly feasible for a Xantia alternator to be low on brush pressure.

[Mandrake]

When taking off or refitting the idle stepper motor, you MUST first disconnect the battery. This stops the unit being energised until you turn on the ignition & the ECU can then reset the parameters for the motor.

It is advisable not to go poking around or pulling/pushing the piston, as the circuitry that controls the motor is quite delicate. For cleaning, get some electrical switch cleaner as this will clean any dirty internal contacts, without leaving a residue & lubricate the internals. If you own a Citroen, its obligatory to keep a tin if switch cleaner.

H

Are you referring to the OP's 2 litre or my 3 litre ?

The ICV valve in the 3 litre V6 is not a piston type, nor a stepper motor type, its a pulse width modulated two phase rotary solenoid that rotates only up to 90 degrees to control air flow.

[citronut]

The ICV valve in the 3 litre V6 is not a piston type, nor a stepper motor type, its a pulse width modulated two phase rotary solenoid that rotates only up to 90 degrees to control air flow.

Simon my findings were with the normal stepper motor type and i have had no experience of the type you describe,

as Richard says the normal stepper motor type are very very delicate, and probably would not like being yanked and pulled around

[addo]

Trust me, pull one apart and have an Uncle Merv. You can see how the rack indexes; there's nothing fancy to it all.

[CFO]

Hi folks - the narrative for my particular fault on the 2litre engine with the Magneti Marelli fitting becomes clearer with the subsequent discussion (and having dismantled and cleaned the throttle body)

I imagine that the original problem of stalling on idle arose because the piston in the inlet air valve was sticking and not withdrawing sufficiently to admit inlet air when the main butterfly valve closed. When we took the MM off the car, we didn't disconnect the battery, but we did manage to move the piston to check for free movement, so on reassembling we had lost the setting and the hunting occurred because the ECU couldn't find the correct position for idle speed. We finally cured the problem by disconnecting and reconnecting the battery which forced a reset of the initial parameters and correct idling was restored.

It all seems so logical after the event.

And for this newbie, what is OP and Uncle Merv, please?

Fraser