Technical 1.6 - unsteady tickover

[schlau2]

Hello. I have this kind of problem. It's about 630-670 prm(I've connected the elm327) and the engine works very unsteady. Sometimes it sticks on 2000prm or floats from 600 to 1000(very rarely). When I turn on the aircon the prm boost and engine works better but not so smooth. I've tried to change spark plugs, to clean injector, to clean and relearn the throttle(from forum's guide) but it doesn't help.
Sometimes the error appears "lose connection coolant temp. sensor failure".
I have Stilo 1.6 02
The examiner says that everything is ok(no errors. coils, lambda, etc. is fine) so the serviceman couldn't help me.
Please help!:worship:
p.s. sorry for my English

 

[Deckchair5]

Engine temp sensor tells the ecu what fuel to put in so I'd check that out as your car is already telling you there's a problem there. Might just be a poor connection at the sensor. Look in the Stilo Guides for checking your engine temp sensor

 

[schlau2]

Thanks, I'll start with coolant sensor.
Is it that sensor? https://www.fiatforum.com/stilo-guides/104106-testing-radiator-fan-engine-temp-sensor-circuits.html

 

[Deckchair5]

Yes, use the information there to help you test if the sensor is producing the correct resistance ( it more often is ok) or whether the connector to it has a poor contact

 

[Barry_M2]

Hi mate, I have a spare coolant temp sensor that will fit your engine (1.6). I brought it in error as I wanted to replace the one on my 1.8.

Anyway, I still have it so it's yours for free if you want it?

I replaced the coolant temp sensor on mine and it seems to have sorted out the rough running which used to occur about 2 or 3 mins after starting up.

I assumed the ecu was getting an incorrect reading from the coolant temp sensor and fingers crossed I was right, as it seems to be behaving its self now.

If you PM me your address, I'll bung it in the post to you.

Takes about 2 mins to change.

 

[schlau2]

Yes, use the information there to help you test if the sensor is producing the correct resistance ( it more often is ok) or whether the connector to it has a poor contact

Thanks. Maybe have you more ideas? The error "lose connection" appears rarely but unsteady tickover is constant.

 

[schlau2]

Hello again. Still no success. Maybe anyone knows when I replace the coil do I need to do something with examiner(like relearn when replace the throttle body) or not? Thanks!

 

[Deckchair5]

No, once you have replaced the coil then the warning will clear after three clear starts wth no need for Examiner.

What checks did you do with the engine temp sensor?

Are you sure you've cleaned the throttle valve properly?
Any exhaust leaks as these will cause tickover problems?

Did it always use to tickover ok?

Have you done any modifications to the air intake?

Have you checked out your lambda sensor?

Are there any stored fault codes?

 

[Nello]

Have you tried this?
https://www.fiatforum.com/stilo-guides/83260-cleaning-your-inlet-control-valve.html

 

[schlau2]

What checks did you do with the engine temp sensor? - checked the contacts. The error doesn't appear anymore

Are you sure you've cleaned the throttle valve properly? - It was cleaned by the service and relearn by examiner, but I want to reclean it by myself

Any exhaust leaks as these will cause tickover problems? - good idea, will check it

Did it always use to tickover ok? - sorry, don't understand it..

Have you done any modifications to the air intake? - no

Have you checked out your lambda sensor? - by examiner it's in good state(how can I check it manually?)

Are there any stored fault codes? - no, there are no stored errors and it's the main problem...(except the unstedy tickover of course)

Thanks!

 

[Deckchair5]

Are you sure you've cleaned the throttle valve properly? - It was cleaned by the service and relearn by examiner, but I want to reclean it by myself

Yes, do it yourself
Did it always use to tickover ok? - sorry, don't understand it..
I mean has it suddenly started to be a problem or have you bought the car with the probelm already

Have you checked out your lambda sensor? - by examiner it's in good state(how can I check it manually?)

You can check it's output voltage even with a simple multimeter and see if it's responding properly at tickover. It should swing from high to low every few seconds. You'll need to back probe the lambda sensor connector to do that. Look in the Stilo Guides for how to test electrical circuits

But go for the throttle valve first for if the valve movement is sticking then it can't possibly keep a smooth tickover

 

[schlau2]

I mean has it suddenly started to be a problem or have you bought the car with the probelm already

I've bought it with this problem(serviceman said that it common problem with throttle and he will easily solve it... liar)

You can check it's output voltage even with a simple multimeter and see if it's responding properly at tickover. It should swing from high to low every few seconds. You'll need to back probe the lambda sensor connector to do that. Look in the Stilo Guides for how to test electrical circuits

But go for the throttle valve first for if the valve movement is sticking then it can't possibly keep a smooth tickover

Thanks, after throttle will check the lambda. Can I check it by elm327? If yes which software can I use for it?

 

[Deckchair5]

Go for the throttle valve cleaning first as a Stilo should be able to hold a tickover even with a poor lambda. If the valve is sticking in the hardly open position -just where tickover is- then it doesn't have a chance

Almost all diagnostic software will enable you to read the lambda voltages, some just read out the figures which is still good enough but no different to connecting a multimeter directly to the lambda connector, others show a graphical trace so it's easier to spot problems. I do just as well with just a simple multimeter back probed and connected directly to the lambda connector

Here I'm testing a Bravo lambda sensor. At warm tickover the voltage should swing high to low (around 0.8v high to 0.2v low) at every few seconds. It's the same for a Stilo

There's 4 wires to a Stilo Lambda sensor 2 for the heater and these are usually the same colour (more often grey) and the other two will be the lambda sensor, usually the black wire is the one for the lambda output

 

[schlau2]

Go for the throttle valve cleaning first as a Stilo should be able to hold a tickover even with a poor lambda. If the valve is sticking in the hardly open position -just where tickover is- then it doesn't have a chance

I looked at the throttle - when I start the engine the butterfly valve opens a little and then it didn't move until I pressed the accelerator pedal. I cleaned the throtthe again but nothing changed.. I tried to disconnect the connector from the throttle - I got the engine fault and revs were on 1100rpm but even then the engine was a little unsteady.

Another question - which brand name of the original coils? Mine are Champion but I found one coil from last owner and it's named Sagem. I tried to fit the Sagem one and nothing changed.

Almost all diagnostic software will enable you to read the lambda voltages, some just read out the figures which is still good enough but no different to connecting a multimeter directly to the lambda connector, others show a graphical trace so it's easier to spot problems. I do just as well with just a simple multimeter back probed and connected directly to the lambda connector

Here is the screenshot from a diagnostic software. Is there a problem with lambda?


Thanks a lot for your help!:worship:

 

[Deckchair5]

Your lambda sensors look good.
Sensor 1
The pre cat sensor is showing fast response and changing from low to high which is good.
Sensor 2
This is also showing fast response and in the right range so the sensor seems fine. What it's displaying isn't normal but that's due to the unsteady tickover.
RPM
Ha! Yes that's a very unsteady tickover!
Did you follow the guide for cleaning the throttle valv and get to clean that area where the flap almost touches the bore surface?

So what to look at next?
Easy ones first
Do you have good spark plugs? Check the plug gaps and if in doubt change them.
Is the air filter clean?
Look for any split hoses on the vacuum side of the inlet manifold.
Do you have any exhaust leaks?
Reset the ecu by disconnecting the battery for a few hours

Coils tend to either work or not and when they don't work you'll have an unmistakable misfire

Has it had any other work done recently like cambelt change?

 

[schlau2]

Sorry for the silence, now I pretty sure that throttle has a mechanical defect as I tried all that can cause unsteady tickover. I found a man who has the same problem and nothing helped. He bought a used throttle body installed it and now it's ok. He disassembled the old one and found out that some parts get damaged(I do not understand what exactly, but he says that it can be repaired very hard) So, could you please advice where I can find a used or new throttle body for stilo 1.6 2002 zfa19200000120227? Thanks!

 

[Nello]

Did u try to clean and actuate the Throttle Valve as per earlier?

 

[schlau2]

Did u try to clean and actuate the Throttle Valve as per earlier?

Of course, I wrote about it. I clean and relearn it by myself and by fiat service. I changed plugs, checked lambda sensors, cam belt, jet fuel, change all filters and other. And there is no result

 

[schlau2]

No one doesn't know??? Where are you buy parts?

 

[Deckchair5]

You didn't answer previous questions
any split hoses on the vacuum side of the inlet manifold?
Do you have any exhaust leaks?
Has it had any other work done recently like cambelt change?

You only show 6 secs of idle rpm on your charts, minimum rpm is shown as 726rpm and not the 630-670rpm you stated in the first post. That's important because your idle is going above minimum rpm and not below it. Can you post any longer times - warm engine- idle rpm - lambda No 1 - aircon off

Throttle bodies only available from Fiat garages or specialist reconditioners or from scrap vehicles. Have to google search for them