I am struggling with my Ulysse which started with the engine cutting out at junctions and at low revs.On the net I tearnt that the ICV was the culprit so i removed it cleaned it with carb spray and refitted.After a lot of weirdness with the engine reving up and down and staying up it settled back to touble free operation.Now its started again cutting out etc.and being so high a tick over i can drive along in second with no feet in use!! Question is there little option but for me to fork out the £90 odd required for a new fiat part? I know this part is a motorised valve controlled by the ecu but does it react to another sensor which tells the ecu (such as temp or something) what to do? In other words could it be another sensor is at fault.Any input from a techie very much appreciated.. Cheers
The ECU implements an idle stategy based on many inputs from its sensors, but in a nutshell the ecu is programmed to maintain idle revs between certain rpm, according to engine temperature, which it will always try to do regardless of engine load. Its a very simple phenomenon in principle, but actually the ecu is manipulating ignition timing in a far more vigourous way to maintain idle speed than it operates the valve.
The ECU will also be monitoring the road speed sensor, as in motion and stationary idle strategies are completely different. As soon as the car reaches around 3mph you should see the idle speed rise by 100rpm or so.
ISCV's do have a finite life, and assuming you have not got extranious air leaks around the throttle body or inlet manifold, I would guarrenteee that your valve is knackered and sticking at certain points in its travel, and should be renewed.
Your strange revving behavioiur after cleaning the valve was almost certainly the ECU getting confused and having to re-learn its idle trim values, as the now clean valve was admitting more air than it previously was. Always disconnect the battery to force it to completely re-learn from scratch rather than stored values in future. I assume you properly cleaned the throttle body at the same time you cleaned the valve. This is most important- the throttle bore should be clean enough to eat off and not caked in carbon and coke, both infront and behind the throttle disc.
If you were to scope the ISCV wires, in your application, you would see that the ECU drives the valve shut inversely proportionally to throttle angle as the throttle opens, so at anything over around 2000rpm the ISCV is totally shut.
In some applications (i.e. Ford) this isnt the case, and the ISCV mimics the throttle, and so suppliments the throttle valve for air admitance, for two reasons, a) to provide good smooth drivability at low speed coming on and off the throttle, and b) for emissions purposes. My focus for instance motors the valve almost fully open at cruise conditions, then when the throttle closes, the ecu cuts the fuel but keeps the iscv fully open, to reduce pumping losses- engine breaking is pretty much non existant. As revs drop the valve is progressivly closed down to about 1600rpm where upon it begins to fire the injectors once every other power stroke, then below
1350rpm it reverts back to fuelling for every power stroke.
Hope this gives you alittle more knowledge into understanding your problem.
Hi Tim Many many thanks for all that some a bit over my head but i get the gist.One more question please. Last night the car kept acting as if the engine had been turned off for a second with a kangaroo effect on the passengers then it would clear and the return at diff speeds but especially low.Could you put this down to the valve opening slightly at the wrong time.It felt like an electrical spark fault.
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