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Full Version Magneti Marelli - Idle Instability

Club XM Forum > Petrol Specific Issues
Michael P
I have a S1 with the Magneti Marelli system. My idle is always unstable and at times the symptoms are that bad that I am not able to start the engine at all as the it just cuts off. If I keep the foot on the pedal it keeps running normally but dies as soon as I take the foot off and the main flap closes. That happens whether the engine is warm or cold. Never I get the ECU warning light to come up. The problem seems to be intermittent and may just disappear. I believe I have cured it once or twice by wiggeling the pressure sensor, the throttle flap pot and the air intake sensor connections. But I don't know what or why because as I did this on other occasions it wouldn't cure it.
The only way I can drive the car when the symptom is present is to bias the trottle cable such that the flap is open enough for an artificial idle. This is obviously not so nice as the idle speed is then about 1500 or so and going down a hill in gear is a new experience. I downloaded this fault code file but as there is no light on, would there be any fault detected int he ECU at all?
Obviously it is an electrical fault but I am not really sure where to start looking, especially since it is intermittent and all the contacts look essentially like new. ANy hints?


Hi. Michael.

Autodata list the following check sequence. Eng. XU10J2, Marelli. Don't know how much is pertinent to yours, but here goes --
Check Battery and Engine electrical connections
Check Evaporative Emission canister purge valve
Throttle cable adjustment
Induction system and vacuum system -- check for leaks
Engine coolant temp. sensor
Idle speed control actuator
Idle air control valve
Throttle position sensor
Intake air temp sensor
Fuel pressure / holding pressure
Exhaust sysytem before Lambda sensor -- check for leaks.

Barely ten minutes work !! Hope some of it helps.

Michael P
Well, that provedure is great if you know the values of all the sensors and I suppose it is published in the book you are mentioning.
The problme may be the wiring as well. As usual it will probably lurk in some kind of connection. There is no lambda sensor in this system, but thanks for your help anyway. Without more info about the sensors I can just do a visual and a very minor electrical inspection. That is more or less what I have done already.

Thanks very much, Michael

Idle valve definitely OK.
Check Evaporative Emission canister purge valve: sounds cool, what is meant?
If you're still looking at this problem, it'll likely be the air control valve - it's a piston type and it sticks. Remove it, strip it out and clean it well with carb cleaner or petrol and then re-fit, should sort it for a while. Used to have to sort mine every 6 months or so. There used to be a plunger kit for them.

Also, found that if you disconnect the hose that runs from the air cleaner to the valve, spray lots of WD40 down it and then turn ignition on/off a few times and then start, it may solve it for a short while. That'd show it was the valve at least.

Hi Michael,

There's a few things it could be but the only two I can think of which wouldn't result in the engine management light coming on :

1. an air leak after the air flow meter

2. the sticking air control valve (as Dave says)


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Hi Michael,

I don't know if you got your problem fixed or not but here's the Magnetti Marelli manual for the injection system.


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for some reason I can't upload pdf's. Change the filename extension to pdf before opening.
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