(T) 1.8 MW : weird idle behaviour

Hi,
my 1-yr-old 1.8 MW Stilo has been quite well behaved, but since a few weeks i have started noticing a weird behaviour of the idle.

If the car is NOT moving, the idle sets nicely at 900RPM, and if I give and release the accelerator, the RPMs go up and redescend gradually to 900 RPM. Everything works just fine.

BUT: If the car is moving and comes to a still (e.g. at a trafic light), then the engine first drops to 900, then goes up to ~1500 for a couple of seconds, then settles back to 900RPM.

Even stranger: if I stop the car on a small downhill with the engine running idle, and then release the brake, as soon as the car start moving the idle goes up to 1500 WITHOUT ME TOUCHING THE GAS PEDAL!!!. If I brake and the car comes to a stand, the engine drops back to 900 RPM.

The last funny thing is that if I put the car on flat land and the 2nd gear in, the RPMs go up to 1500 and the car moves by itself, without me pressing the gas pedal. (poltergeist?)

I initially though there might have been some dirt somewhere, but this would affect the idle independent of whether the car moves or not. To me it looks more like a "logic" thing, as if the computer did not want to let the RPM drop unless the car is idle (e.g. in case power is needed for the brakes or the steering).

Has anyone out there experienced similar behaviours? or woudl anyone care to test the situations I mentioned above and let us know if this is a bug or a feature ;-)?

thanks & best regards!

to the forums!

I've not heard of any such problem to date, but if others have they'll post up their help soon!

Hey.. have you had an air filter fitted or a service recently?!

Even if not.. ...it could be a possibility that your airfilter has come lose; because i had exactly the same kinda problem on my punto! The problem i had, was like you sed above, the car wud drop to its normal revs as you say then like started reving its selfing and pulling when i pulled off! The airfilter had jus come lose; once connected/tightened back up, perfectly fine.

Have a look and see if that sorts the problem!

Hi,
thanks for the hint. I will have a look. However: do you recall if you had this problem (assuming this _is_ a problem) both when the car is at a still or while moving? A airfilter come lose would presumably give troubles independent on whether the car is moving or not, while in my case if the car is not moving everything works perfectly OK...
Cheers

i had the problem when the car was still and moving?!

Are you sure its idling at 900rpm when it seems ok, that still seems high to me, my car idles at 750rpm or there abouts.

my 1.6 idles @ 750rpm. You need to remember that the revs fluctuate all the time (by varying degrees) the engine management system is constantly trying to keep revs low at idle for emmissions purposes, but on the other hand is trying to keep it above stalling. If you are in a queue of traffic, in 1st with the clutch down, and you SLOWLY take your foot off the clutch the car will drive itself forward without you pressing the accelorator, it works in 2nd & 3rd aswell - it's the engine management system keeping the engine from stalling.

What kind of gearbox do you have? (is there a semi auto box available?) Do you tend to let the car move along under tickover revs often? Say when stuck in traffic. If you do, the ecu will attempt to keep the car from stalling, and give the engine more fuel, when you bury the clutch to stop the revs will shoot up, until the ECU senses that there is no load on the engine, and then the revs will drop. If it's a semi auto 'box this is most likely to be the cause, especially if you experiance this after being stuck in slow moving traffic.

The airfilter problem i had was on my punto! By ne.ways...

After reading what your motors idle at i checked mine out and it idles @ 1100rpm all the time when in standing still. I have a 1.8 dynamic

This seems quite high compared to other posted or is this normal for my model?!

Pretty much all cars should be able to drive without touching the gas pedal. However the Stilo has a very good anti-stall built into the idling system. You can make a fluff of it and have the revs down at 200rpm and the engine will rev itself up a bit to stop you stalling.

When it's idling at 1100rpm is the engine cold? It will normally idle this high from cold and gradually come down to about 750rpm as the engine warms up. Like having the choke out on an older car. If yours is idling at 1100rpm when it's warm you almost certainly have a problem.

Oh yeah! y didnt i fink of tht, yer wen i was looking at it! It wer r=first thing in the morning when i just started using the car! Doh!

Hi,
here is an update to the problem description I made a few days ago. First of all a general comment; I erroneously mentioned that the idle is about 900 RPM, but indeed it has always been at 750~800, as you correctly suggested .

Additionally, it seems that since yesterday the behaviour of my Stio at idle has gone back to normal.

I.e. the strange "up and down" of the idle after coming to a stop (e.g. at a trafic light) has now disappeared, and the engine just drops to idle and stays there. (earlier it used to jump back to 1500 and re-.descend after a few secs. )

Also, the idle remains stable at 750~800 when the car runs downhill in neutral gear or with the clutch pressed. (earlier, the idle growed to 1,500 all by itself).

The mistery remains on the causes of the strange behaviour I had reported in my original post. Maybe some sensor sent distorted information to the computer? Or some dirt created some problem? Big mistery.

Cheers!

Hi Chestnut, are you also on the Italian Forum?
I have replied there and it makes sense I think.
It is just a reaction of the ECU to the actual engine temperature.
It is abslutely normal in cold climates.
Full details in my reply on the Italian STC forum.
Ciao!

Your car will be having a nervous breakdown if you coast downhill in gear with the clutch depressed.