Hi to all reading this, I need you sincere help and advise!
My Stilo 1.6 petrol with LPG system installed has some issues with idle and low RPM up until to 1500 range. Not so much of a ruff idle but a strange behavior, let me explain.
I own a Stilo 1.6 petrol, year 2002, 5 door sedan. We bought the car second hand from a dealer this year in February, we drive it since but from a month or so ago with a little behavioral problem with low and idle RPM. We installed an LPG Landi Renzo system into the car immediately as we bought it, the job was done easily and professionally, no troubles with it what so ever. The car after we bought it has undergone some mechanical fixes the drive belt set has been changed, new front suspensions, new rear silent blocks, new clutch set and a gear linkage fix, new tires, oil change and the usual major look over. It threw us back money vise quite a bit but since we bought the car to use it day by day and to travel around in it safely I wanted it to be in shape. We've drove more than 8000 km's in it so far without any major fault. Mechanically it's rock solid. We drive it around town and on a freeway as well, it performs nicely, the consumption is perfectly normal and OK and it serves us well but...
But one little annoying problem came up from a month or so ago and I'm yet to find a solution for it.
The problem is that our Idle RPM variate's some 150rpm's which is so much that it can be felt even at low RPM's up to 1500 when accelerating. It does this on Petrol and LPG as well, it's felt less on Petrol and more on LPG but it's doing this RPM fluctuation (that's the perfect word for it) occasionally and for random amounts of time. It does this some time when cold or when at running temp, more on running temp and the RPM fluctuations are not constant this is the most strange thing to me, they come and go intermittently for some 30s to a minute then Idle RPM becomes rock solid again, then it's doing it again and so on...it's driving me nuts why is it doing it, the most annoying is when accelerating and the car's engine's RPM's are audibly fluctuating, it does not stall or shut down, it just fluctuates.
Fixes we tried so far:
1. Spark plug change - Nothing.
2. Intake valve complete clean and run through - Nothing
3. Used up 2 or 3 cans of various brand "magic" injector and carburetor cleaning petrol additive (Wurth, Wins, etc) and drove some 2000km's on petrol - The running is a bit smoother and quieter but the rpm fluctuations remain without change.
4. I bought an OBD2 tester just to check for engine faults - No registered Engine Faults or errors of any kind.
The car seems rock solid and working, I told you, we drove in it already some 8000 km's without any major hiccups except this very annoying RPM fluctuation at Idle and at low RPM's.
It has seen 2 mechanics so far, neither of them could tell me what's wrong, except that mechanically the car is sound and ideal. It went back to the LPG service where the LPG system was put it, they ran diagnostics and some basic check ups and of course they tell me the same that the system of theirs is working flawlessly and it's NOT the LPG system causing it.
They tell me it's obviously the dodgy Italian electronics somewhere in the car but they of course are not electronics themselves so they could not tell me more
I'm getting frustrated about this RPM fluctuation. We can still drive the car but it's annoying, it just begun to appear and it has not gone worse, it's just there, sometimes it makes the engine rev over or louder sometimes the rpm's are steady but more times it's not that's for sure.

Has anyone experienced anything like this so far? Does any one of you guys have similar Stilo with LPG in it and did anyone notice something like this? I'm in desperate need of help.
I really like the car it serves us well and I feel if we take care of it, it will take care of us as well but this annoying rpm fluctuation is yet to be fixed.
Any suggestions are welcome!

Hi guys, updates on the situation.
I took the car to the LPG service today to check out why did the LPG system just suddenly shut down while driving and switch back to Petrol. The car drove fine, we were on a highway, the LPG tank was full and later half full when it did this.
I know there is a fail safe built into the system if it senses some major fault than it will just shut off the LPG and return to Petrol dynamically, but since it did not do this kind of behavior yet I took it to the shop.
They read out from the LPG's computer that there is probably a fault with the MAP sensor.
I was scratching my head because the ECU of the car did not register a MAP sensor fault but the LPG system did.
Thou I got an Engine Fault and a yellow engine light on the dash when accelerating in 4th gear on the highway while on LPG.
I checked the fault codes, they read:
- P0420
- P0136
These two are Catalytic converter sensor signal below threshold and Downstream O2 sensor signal below threshold. These two specific errors constantly keep showing up ONLY while driving on LPG. They never ever once showed up while I drove the car on Petrol, solely on LPG. As far as I know this is a known issue and I'm yet to find fix for it, but some people just tell me to drive it like that since the car was not meant for LPG and that's why it is sensing a wrong fuel mixture.

Back to LPG, I took it back to their garage 4 or 5 times now to check it out, they just turn heads saying their system is fine... while I'm like AAAAA :bang: Incompetent people... I'm fed up with the ping-pong-ing from a mechanic to a mechanic.
That's why I'm posting here maybe someone out there has an answer to my troubles or a fix to the issues with the ruff idle and the LPG systems errors.

Tomorrow I'm taking the car back again to the LPG shop to check out whether it's really the MAP sensor, I doubt it, I'm an electrical engineer, I know my way around electronics a little bit that one specific peace of sensor on the car seems fine to me, according to the ECU of the car it did not register an error, at least not since I have it.

Well, wish me luck who ever is reading this, fingers crossed for what the LPG guys are going to find in the morning.
I'm hoping only the best

Sounds like an issue with the car, and not LPG system going by your first post. The sensor may be within tolerance for the cars on Petrol, but obviously isn't perhaps for the LPG system.

Not what you want to hear but the 1.6 is a poor engine in the Stilo when Petrol only, nothing but problems IMO, adding LPG is only going to complicate things. What LPG system have you had fitted? Just hope you went for something decent like BRC or Prinus or your again asking for trouble unfortunately.

I've a Stilo, which to date has done 57000 miles on LPG without fault, mines a BRC system on a 1.4 mind.

Jon.

Thanks for the reply Jon,
The LPG system in the car is a Landirenzo (Italian) www . landi . it I know what you are going to say but...we had to go with the budget kind hoping it wont turn out too bad.
The car in it self (except this strange fluctuating RPM issue) is sound and a nice experience to drive. We drive it on mixed roads, town and highway as well, I've even been to the mountains with it with passengers and luggage and it behaved totally OK.
As I wrote earlier the consumption is ideal (mixed conditions), it's 7L of Petrol on 100km or 10L of LPG on 100km (to add I seldom ride alone, usually it's wife and little daughter as well ) and AC on since we are having quite a hot summer in Serbia So taken all this into account I think it's not eating more petrol or gas than it should, the engine when idling sounds good, no tinkling or strange sounds. It does not die on us, it never left us on the side of the road so far Mechanically it should be all OK but there is that one small unperfection that little "umpf" I would like to sort out which is this thing with the fluctuating RPM and a small hesitation when accelerating.
My mechanic told me literally that I made my biggest mistake in life when I bought a Stilo, and I made my second biggest mistake in life when I put LPG in a car I should not have purchased He is a funny bloke...ok he speaks from his own experiences, he prefers VW's, Opels and Fords before anything else just out of experience, but after a lot of reading and we trusted (he is a family friend) the dealer we bought the car. They tell me all dealers are the same, family, friend or not, and it is true to some extent they have one thing before them and that is to sell the bloody vehicle, but still...he told us the things that needed to be fixed, they were all done except this one annoying issue with the strange RPM fluctuation. At least we got the car for a very good price here in Serbia.
Around 70 to 150 rpm's it fluctuates around idle and it does this when accelerating so much that it can be heard and felt in the low RPM ranges, later on it smooths out and the car drives just fine and it's responsive too.
I will search, read, experiment and try out suggestions as long as this does not get fixed, I'm a little bit a perfectionist and I cannot just simply leave it at that I'd like it much more sorted out.
I'll update when the car tomorrow sees the LPG guys and the mentioned MAP sensor check up.
Cheers
Zoli

It might be worth disconnecting the battery for 30min or so to reset everything incase it is a small electrical glitch.

I hope you manage to get it sorted. Keep us up to date

Have you tried the throttle re-learn procedure on it yet? Could just a slight breakdown in communication at some point between the ecu and throttle body causing slight fluctuations in the throttle butterfly, I'll try did out the relearn for you

Got it! Post #7 is what you'll want to look at. Try that and see if it cures it Might also be worth removing the MAP sensor nd cleaning any build-up of dirt on its surface, even if that won't cure it it will still run a bit smoother and possibly improve mpg

Some good news and some bad news I have for you Isn't this always the case
I went to the LPG service, they tell me that the reason why the LPG system cut out and went back by it self to Petrol is most probably the MAP sensor or the LPG system ( I did not know it had one of it's own ). They lift up the car, take off the faulty MAP sensor of the LPG system and voila they show me how and where it's faulty, it was a factory fault with those models, even the manufacturer Landirenzo from Italy has noted the issue with the specific model and they change every one of these faulty MAP sensors under warranty.
It was just two screws, on came the new one, car down and I drove home without a glitch.

The bad side of this is that I'm still left with the uneven low RPM that is fluctuating a bit.
I did the throttle body re-learn procedure, at least I hope it was that !?
One of the first things I did was to play around with the key set to MAR, leave it for 1 min, then turn off, wait at least 5 seconds, then turn on and leave it to idle a bit, then turn it off the on again.
It did squat, nothing, zero, no change what so ever. Hey at least it did not get any worse right
Then I tried the Self Adaptation reset procedure using Fiat's ECU Scan software (version 3.5). I't completed it perfectly. It did nothing to fix the uneven low RPM's.
My mechanic told me a few months ago when he cleaned the throttle body that it's little motor is on it's way out, apparently it's jamming the axle of the flap a little bit, just enough that it can (he did not say that's the reason 100%) cause this strange rpm issue or it could well be the potentiometer of the throttle body as well.

In any case thanks guys for the advises so far, what I can and will do at home is to have a look at the MAF sensor of the car, clean it also the MAP sensor and clean that as well. I'll have time in the other half of the week to toy around with it so I'll post my findings then.
If those do not fix the problem I think I need to look up a good car electrician who knows his way around Fiat's (I'm becoming a viz for Fiat Stilo's my self because of the lot's of reading and trying out on my car ). The Stilo is our first car ever and I'm an electrical engineer, I like to think that whatever humans built can be fixed! A man built it, a man can take it apart and fix it as well.
I'm not a car mechanic, I know car's are not fixed by reading and posting on forums, but I try to get involved as much into the workings of the car as I have time and knowledge so that for 1. I cannot be fooled by some mechanic or service guy who think they are know it all's, for 2. I understand why is what happening in the car so I know the remedy or at least to whom should I take it.

If all fails and nothing else changes the behavior of the car I need to take it to a professional, I'm out of ideas.

Thanks guys so far,
I'll keep you updated.
Zoli

Hi guys, thought of posting some updates about the situation of my strange idling problem Stilo. I still like the car that has not changed, actually I still want to make it better and fix it since I grew fond of the little vehicle.

As said earlier the idling unevenness or idle fluctuating rpm is intermittent. I mean by this that it does it only for periods, than it's again rock solid idle for a 30s or a min then again it goes haywire then it gets solid again end so on.
I noticed a few things:
- It does it less when the engine is not yet at working temperature
- Just before I notice the fluctuating idle rpm I think I can hear a small "tick" sound from the engine somewhere, like a relay clicks, I'm not 100% but it sounds to me like that
- If the car is doing the fluctuating idle rpm and I turn on the AC or the cooling fans turn on that usually puts added strain on the engine and that evens out the rpm's, it basically stops fluctuating or is barely noticeable

The more I think about it the more it seems to me to be an electrical fault somewhere. Strangely enough no related OBD codes or Engine Faults happening what so ever. The car drives not perfect but fine. It seems to me like it lacks a little "umpf" of power when pulling, I kinda feel that am empty car with only me in it with a 1.6L engine without AC on and on an even open road should accelerate faster, with more power. Maybe I'm mistaken, but I've driven a few other cars in my life, not for long thou since this is our first own car, but I still get the feeling that like something is holding back the little Stilos horses so they don't develop full torque.

The sad thing in this is that I need to have him checked out by a proper mechanic or electrician since we need to go through the complete Intake, Petrol Injection, and Output systems for a complete check-through. Air filter, MAF, Butterfly Valve, ... Cylinder pressure, Lambda sensors, Catalyst (it may even be a clogged up catalyst who knows ?! ), exhaust...

Waiting for a little bit of money to build up and I will take him to hopefully someone who can do all these check ups for me and won't cost me a fortune.

People have built this car and people can fix it I'm sure! I just need to find the right person

All right, I'll keep you posted about my findings and If I locate the cause of the issues I'll definitely tell you.

Regards,
Zoltan

Hello forum "dwellers"
UPDATES regarding my situation with our Stilo 1.6 with LPG installed.
Finally I had the time to fiddle around with it a little bit to try to resolve the annoying thing with the sometimes ruff idle and poor acceleration.
What I did is to look over the general sensors on the intake, MAF, Throttle Body, MAP and a few other small things.
I also have driven into our little Stilo, by the way which I like very much hence my will to fix it and know it's as good as possible, something over 13000km's from February 2012, since we bought it.
So it was well time to take it for an oil change, filter change and general look over. Once that was done I took it to a local car electronics garage dealing with all kinds of electric fixes and upgrades and they also had a go at it with some professional diagnostic equipment and the verdict is (you are going to feel some irony in this I hope):
2 independent mechanics, first the one who did the initial oil change and fix up, and then secondly the upcoming oil change garage, they both tell me that the car mechanically is as sound as a kitten, it purrs and nothing serious is wrong with it mechanically and they both said that little annoyance of the ruff idle and poor acceleration is surely an electronic fault. The one electrician who had a look at it with a professional diagnostic equipment says that ALL the sensors even when looking at their signal with an analog device seem OK and nothing is needed to be fixed, and that small flaw of ruff idle is surely due to some mechanical fault are you feeling the irony here ???
And when I take it to the 4th garage where the LPG was installed they just lift their hands, saying that this is definitely not their fault
God damn... I'm sorry but I'm pissed ... world with stupid garages and mechanics and know it all people.
So the verdict is that nor mechanically nor electronically nor in the LPG system is there any fault, at least nothing mayor or detectable.
I also figure if there is a fault, at least I hope, it should be something small, either a leaking gasket or some false air intake somewhere ...
The important thing is that we have driven 13 thousand km's into our little Stilo with my wife, the car never died on us, it never gave out and we'w been to Greece with it in the mid of summer with over 40C outside, I've driven it around Slovenia, Croatia and Serbia in hill'ish countryside and in the mountain range as well and on the open road it drives perfect, no flaw, no issue or engine fault.
In the city with usual low frequent gear changes mostly in 1st 2nd and 3rd gear it kinda hesitates with acceleration and sometimes the low rpm's ar uneven.
That's it. It's something that bugs me a lot, but I think I'm going to have to live with it at least for now.
If I ever finally manage to resolve it fully, I'll definitely let you all know!
Thanks for the help so far!
Best regards,
Zoltan

One of our friend had similar problem, rough idle and poor acceleration in the lower rpm. No error code has been thrown. When the car is cold there is no vibration and unsteady idle but as the car warms up we had this issue. Once the Oxygen sensor socket is disconnected all vibrations has been vanished. Later with new sensor the car is good. Ear that car had MAP sensor change but the unsteady vibrations were present.

Hi, thanks for the info at this point anything that would or could help is appreciated.
Regarding the lambda (oxygen sensor) I'm told by a car electrician that it's signal output is fine.
I am an electrical engineer my self thou I'm not good at car electronics (but hell I'm becoming one ) and I also suspect that maybe the oxygen sensor signal output is "sluggish", I heard that over time the responsiveness of the lambda sensor drops and this can or could cause similar symptoms.
Take a look at this picture I took of the signal output of the pre and post cat lambda:
I don't know is this a good working lambda or not thou I suspect that the post cat lambda should not follow the pre cat lambda, more it should be relatively flat signal compared to the first lambda... I'm not a car electrician I don't know.
Anyone any info regarding this ? Appreciated!
Zoli

you really need to add engine temp and revs on that graph... the pre and post cat lambdas should trace as per 23.8-44.5 secs id be a little worried about the LARGE deflections on the post cat trace like the ones 0-23.8secs and 44.5+ secs. from my experience it would suggest Cat issues... do you have/have you had

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

stored or active at any time by any chance??

richydraper said:

you really need to add engine temp and revs on that graph... the pre and post cat lambdas should trace as per 23.8-44.5 secs id be a little worried about the LARGE deflections on the post cat trace like the ones 0-23.8secs and 44.5+ secs. from my experience it would suggest Cat issues... do you have/have you had

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

stored or active at any time by any chance??

Click to expand...

hi, actually that exact obd error i keep receiving as stored, never active so far. i had that p0420 error appear a few times now, oddly only when the car was running on lpg, never have i noticed it on petrol, and more precisely i usually noticed it when the engine temp was normal around 94C and when stopping and starting again the lpg system kicks in after just few revs of the engine, thats the point i think the cars ecu or the lpg ecu does something goofy and the error is stored. im told by more then one mechanic that this is due to the lpg kicking in (starting) and for a brief moment the car registers an error. never the less, i'll do another graph with engine revs included. this was at idle or during idling when engine is warm. im still to see a proper mechanic who knows how to see and read oxigen sensor signals properly.

P0420 is only set when pre and post cat sensors are tracing 'too closely' in relation to each other as your graph shows... it suggests the cat has a damaged, missing or has an inefficient monolith. (i get it on my 1.6 because the monolith is destroyed BUT in your case, it *could* be a failing post cat lambda)

you could let it develop and i would expect to see the post cat lambda eventually tracing to ground i.e 0.0v. my next step would be to scrutinise and/or replace the post cat lambda because we know its traces aren't right on MES.

please do post lambda traces with engine speed and temp! maybe one on petrol and one on LPG if its possible. so we can see the difference, if any, on the different fuels!

taken from http://freeautomechanic.com/ho2s-heated-oxygen-sensor.html

Heated Oxygen Sensors (HO2S)

OPERATION

The oxygen sensors supply the computer with a signal that indicates a rich or lean condition during engine operation. This input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from one or more sensors indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition). The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles. Heated oxygen sensors are used on all models to allow the engine to reach the closed loop faster.

A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.

Related Symptoms

Surging at idle
Unstable idle
Running rough off idle
Hesitation
Stumble
Chuggle
Poor fuel economy
Spark knock
Stalling on acceleration


TESTING

WARNING
Do not pierce the wires when testing heated oxygen sensors, as this can lead to wiring harness damage. Backprobe the connector to properly read the voltage of HO2S.When testing the oxygen sensor voltage signal, it should correspond to the values shown in this chart

Disconnect the HO2S.
Measure the resistance between PWR and GND terminals of the sensor. If the reading is approximately 6 ohms at 68°F (20°C), the sensor's heater element is in good condition.

With the HO2S connected and engine running, measure the voltage with a Digital Volt-Ohmmeter (DVOM) between terminals HO2S and SIG RTN (GND) of the oxygen sensor connector. If the voltage readings are approximately equal to those in the table, the sensor is okay.



REMOVAL & INSTALLATION

Disconnect the negative battery cable.
Raise and safely support the vehicle on jackstands.
Disconnect the HO2S from the engine control sensor wiring.
NOTE: If excessive force is needed to remove the sensors, lubricate them with penetrating oil prior to removal.

Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A. To remove an HO2S, detach the vehicle wiring harness connector from the sensor wiring harness . . . then remove the sensor from the exhaust system
To install:

Install the sensor in the mounting boss, then tighten it to 27–33 ft. lbs. (37–45 Nm).
Reattach the sensor electrical wiring connector to the engine wiring harness.
Lower the vehicle.
Connect the negative battery cable.

Click to expand...

the wiring designations are as follows
white:- Heater Element
white:- Heater Element
grey:- GND
black:- SIG

heated lambdas only have a life span of between 50,000-100,000 Miles (80,000-160,000Km)

you're testing the lambda to make sure that the readings you are getting from the sensor match that of what the ECU is reading.

hope this helps a little bit

Thanks richydraper for the info and help, I did what you asked me to, I took measurements on LPG and PETROL separately, both while idling and during normal city drive condition.
Please have a look at them, I included engine temp, engine speed, post and pre cat lambda signals.
Measurements on PETROL during idling

Measurements on PETROL while driving

Measurements on LPG while idling

and Measurements on LPG while on the go

Take a look at them. I hope i got the resolution right so you can just about to see the parameters.
If you'd like me to send you the CSV files of the measurements I can do that as well, just drop me your email in a private message.
Thanks in advance!
Zoltan

i think your post cat sensor is dead, its tracing to GND... id also expect to see it having a slow transition time but without an ociloscope, you'll not know, i dont think MES has that level of detail.

maybe someone else can confirm but im pretty sure that lambdas are only supposed to trace 0.2 - 0.8v unless they are shot.

id be expecting to replace the post cat lambda, from those graphs you have posted Zoli, sorry for the bad news

Hi, sincerely thank you for the advice and the info.
Honestly ? I was from the start suspecting on the post cat lambda.
Interesting that neither of the 3 places I took the car for fixing had any clues about or told me anything about the lamdba sensors. They probably didn't even check it, who knows, just told me something to be on my way
This is why I asked the help of you guys and posted on the forum.
I like the car and I'd like to fix it properly.
Sadly this means taking the car to a new place (I don't trust the 3 earlier garages any more) and trying out a new lambda in it. The best option would be to just try it out before ordering it...but not a lot of places keep expensive oxigen sensors for testing right ?
Anyway, I'll give it a go and when I have some info I'll get back to you guys with updates.
Thanks so far!
Zoli

good luck with it Zoli dont forget to come back and tell us how you got on. even if its bad and didnt change anything!

richydraper said:

i think your post cat sensor is dead, its tracing to GND... id also expect to see it having a slow transition time but without an ociloscope, you'll not know, i dont think MES has that level of detail.

maybe someone else can confirm but im pretty sure that lambdas are only supposed to trace 0.2 - 0.8v unless they are shot.

id be expecting to replace the post cat lambda, from those graphs you have posted Zoli, sorry for the bad news

Click to expand...

Sorry mate, but I can't see where on idling graphs is after-cat lambda sensor tracing to GND...