Technical Fiat stilo 1.2 unresponsive throttle

[stilo97]

Hello guys I need your opinion. I have a Fiat Stilo 1.2 ‘03 5 door we bought it new back then. It is a family car very well maintained with no problems until last wear. Out of nowhere the throttle stopped responding and the car stalled. The mechanic said it was giving fault codes from the throttle body so I change it with a used one. For 5 months it was perfectly fine. Then it started having irregular idle I once again went to the shop they took my battery off for some time reconnected it and it was good again. Some months later I was washing the car I took off to return home and the car went in safe mode rpm stack to 900-1000 and no throttle response again. I went to another mechanic he also removed the battery for a while cleaned a ground point inside the engine bay and the car was fine again. Fast forward 9 months from this it stalled again out of nowhere because of unresponsive throttle and the solution was again to disconnect the battery for a while. I have spoken with some shops that specialise in Ecu’s and they told me that it is a known issue for the 1.6’s ecu but not for the 1.2’s ecu. I will have the wiring checked and I hope to find something. Any suggestions about what may be the cause? Or anyone with the same issue ?
Thanks in advance and sorry for the long text.

 

[stilo97]

so I just probe #3 5V with #2 Ground

 

[koalar]

so I just probe #3 5V with #2 Ground

I would probe 3 with battery negative
2 with battery negative

You could have as an example +5 on ground pin and +10 on the 5 volt reference but the difference would be 5v the number you were expecting

 

[koalar]

Interested in the results

Loads of people have had the

P1688

On the Punto as well

There didn't seem to be any definite diagnostic or solution

 

[stilo97]

Interested in the results

Loads of people have had the

P1688

On the Punto as well

There didn't seem to be any definite diagnostic or solution

I will post updates i havent been able to work on it. Maybe later this week i will post with results!

 

[koalar]

Sone of the bravo range uses the same ECU but different throttle body

I found some basice diagnostic from fiat but it would pointless posting them if it's a totally different system

On the bravo with the ignition engine not running, if you press the throttle pedal down the throttle body follows, is that the same on the stilo

I can find dozens of people with the P1688 on the Bosch hybrid ECU

I can't find a single person who has measured and found something

 

[stilo97]

Sone of the bravo range uses the same ECU but different throttle body

I found some basice diagnostic from fiat but it would pointless posting them if it's a totally different system

On the bravo with the ignition engine not running, if you press the throttle pedal down the throttle body follows, is that the same on the stilo

I can find dozens of people with the P1688 on the Bosch hybrid ECU

I can't find a single person who has measured and found something

Just with ignition on the Throttle body responds to the pedal? I havent heard that before i can test it. Tomorrow morning i will take off the egine bay fuze box i will tear it open and give it a good clean i have a feeling that it will be packed with corrosion and dust. I ve also made a new holder for the ECU i will try to take it further away from the block. I will test the ECU connectors for some loose pins and finally i am looking for the rest of the egine grounds to give them a good clean.

 

[Zardo]

Accelerator pedal potentiometer​

Specifications​

The accelerator pedal is equipped with two built-in potentiometers: *- a main one *- a stand-by one.

The injection control unit implements the following recovery strategies in the following conditions:

• if one of the two potentiometers fails, this allows the throttle to be opened to a maximum of 40° over a long time period;
• if both potentiometers fail completely, it prevents throttle opening.

Throttle body​

Specifications​

This is fitted on the intake chamber and regulates the amount of air taken in by the engine.

According to the signal received from the accelerator pedal potentiometer, the injection control unit controls the throttle opening by means of a direct current motor built into the throttle body.

Throttle opening takes place from 0° to 80°, i.e. including idle speed adjustment range. - The throttle body is equipped with two built-in potentiometers, each of which controls the other.

If both potentiometers should fail or in the case of a power cut, the control unit reduces drive torque on the basis of accelerator pedal position.

• with the pedal fully depressed, it cuts off fuel to one or more pistons until a maximum speed of 2500 rpm is reached
• in the intermediate positions, it cuts off the supply to one or more pistons until a lower speed of 2500 rpm is reached.

The self-learning procedure must be carried out if the injection control unit or the air chamber or the throttle casing is replaced.

have a look

 

[koalar]

It's for the brava 594 BOSCH MOTRONIC ME7.3H4M EOBD INJECTION system

No idea if it's relevent to the Stilo

Attached below hope it's readable

 

[koalar]

Home Page

aftersales.fiat.com

 

[stilo97]

have a look

Can it be the pedal potentiometers going bad? Is it possible to open the pedal itself ?

 

[stilo97]

It's for the brava 594 BOSCH MOTRONIC ME7.3H4M EOBD INJECTION system

No idea if it's relevent to the Stilo

Attached below hope it's readable

It’s not the same

 

[koalar]

It’s not the same

I know but it the closest I've got

Am not even 100% on the fault code
P1688 Motorised throttle (2nd idle learn)is listed on the 1.4 16v but not the 1.2

Out of probably 40 or more threads I have looked at the isn't a single diagnosis to fix

The circuit diagrams are often posted but nobody's found anything beeping through

There's one fixed by an ECU but that could be a coincidence, they didn't put the old part back in. Yours was fixed by swapping the throttle body but it didn't last

Pretty sure were on are own

 

[stilo97]

I know but it the closest I've got

Am not even 100% on the fault code
P1688 Motorised throttle (2nd idle learn)is listed on the 1.4 16v but not the 1.2

Out of probably 40 or more threads I have looked at the isn't a single diagnosis to fix

The circuit diagrams are often posted but nobody's found anything beeping through

There's one fixed by an ECU but that could be a coincidence, they didn't put the old part back in. Yours was fixed by swapping the throttle body but it didn't last

Pretty sure were on are own

Let me check with another obd scanner first I got the pro version of the app and it gives me a fake scanner indication

 

[stilo97]

So I open it up today looks pretty clean

but I found some burn marks in the 12V relay I know it isn’t the cause of my problem but a good clean is always needed

 

[Zardo]

Looks like some kind of lego game

play it here

 

[Mike1alike]

So I open it up today looks pretty clean

Next, open the throttle body and give it a good clean.

 

[koalar]

So I open it up today looks pretty clean View attachment 479906but I found some burn marks in the 12V relay I know it isn’t the cause of my problem but a good clean is always needed

View attachment 479907

Top look to be in very good condition

Well done in taking a look

Nothing appears wrong to me

While your this far in

If waters has got in, any corrosion will be on the underside, very rarely the top

Its a long shot, but while dismantled it's worth a look

 

[stilo97]

Indeed it’s a Lego puzzle

 

[koalar]

I can't seen anything obvious that would cause a problem

 

[stilo97]

Guys the copper connector with the 1.2 writing is for the 12V relay right ?