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Old 08-07-2017   #1
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Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Hi,

I have a Fiat Punto 1.2 8v (2004) which sometimes has a really bad, rough idle.

Other than that the car runs fine, there`s no check engine light no excessive fuel consumption, starts quick, drives smooth.

The only problem is when the car is in idle and it`s RPM starts fluctuating noticably. Specially if I put some electric load on the car. Turning on the lights, using the power window.

I already tried to use various fixes with no luck. I went to two repair shops they didn`t find anything. I also went to an official Fiat Service Center. In the service senter they didn`t find the cause of the problem but reseted the ECU and said it fixed the problem. Well, it fixed for 5 minutes. After that it came back again. So I don`t really trust them anymore.

What I already tried:

- Checked the ECU for error codes with an ODB scanner (no errors)
- Reseted the ECU (by disconnecting the battery for an hour)
- Cleaned the throttle body
- Checked for vacuum leaks
- Replaced the idle air control valve (IACV) on the throttle body
- Replaced the whole throttle body form another car
- Replaced the battery
- Replaced the pre-cat lambda (O2) sensor
- Replaced the MAP sensor
- Replaced the spark plugs
- Replaced all ignition coils

I also bought an ODB scanner and checked the car with the Multiecuscan software but couldn`t find anything suspicious. I attach the Multiecuscan logs here. You can check it if you have the free Multiecuscan software. I mark the moment when the rough idle starts in the log. The image only shows the RPM but the log shows many other details as well.
Fiat Punto 1.2 8v 2004 - rough idle - multiscanecu log.csv.zip
Click image for larger version

Name:	 <a href='http://www.fiatforum.com/autolink.php?id=1&script=showthread&forumid=34' target='_blank' title='Fabbrica Italiana Automobili Torino' class='gal'>Fiat</a> Punto 1.2 8v 2004 - rough idle - multiscanecu log.jpg
Views:	90
Size:	181.3 KB
ID:	182163

Created a video which shows the whole problem. (turn on the captions on the video for details)

Do you have any suggestion what I should check? My next guess is the altenator because it happens more often under electric load.
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Last edited by mikeb1; 08-07-2017 at 19:56.
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Old 10-07-2017   #2
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

I`ve just replaced all of the injectors from my other Punto, but the problem is still there. So it`s not the injectors.
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Old 11-07-2017   #3
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Im glad somebody else has this issue....

I have it too... not always replicated on request

I found also heavy electrical load was causing the rough idle to get worse...

My logic was the alternator kicking up hard to generate more power which the engine wasnt predicting and nearly stalling.... hence the up and down bit on the revs

Aircon (on an 8v is rare) would probably amplify the issue too... (make it worse)

Check the condition of the auxilary belt....
I had to replace mine as id lost 2 of the ribs
U having ac will make it more money

Since i havent been able to replicate this since the change i cant confirm 100% it fixed mine

But i do wonder if the fuel pump is lacking pumping power and causes a rough idle? No idea tho

Im yet to see whata actually causing mine

Ziggy
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Old 12-07-2017   #4
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Could you monitor the battery voltage while the engine is acting up? If should be over 13V if all is good. You can do this with a multimeter or should be able to check from the OBD2.

I would be inclined to check the voltage drop between the positive of the alternator and positive of the battery while the engine is running. Do the same for the negative. Should be a very small reading.

I had charging issues before and took me ages to figure out what it was. Turned out I was getting 1V drop between alternator negative and battery negative. Redoing the gearbox ground connection solved the issue. One of the symptoms I had was I used to start the car and it used to rev up and down as if you were pulseing the accelerator. I believe this is the ECU detecting that the system voltage had dropped to a critical point and increases the rpm to generate more charging power. This restores the voltage level. ECU drops the rpm to normal, the voltage immediately drops again and the cycle continues.
This differs from your sysptoms as mines never dropped below normal idle rpm.

If you hooked your battery up to another car while running as if you were trying to jump start and see does it still act up. If it doesn't this would confirm it is a charging problem.
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Old 16-07-2017   #5
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Meanwile I replaced the alternator for a brand new Denso one. The original alternator was charging the battery with 13.95V on idle and did`t want to go more than 13.98V even when I evved the car around 3000RPM.

Now the new Denso alternator charges the battery with 14.05V and goes up a bit when I rev the engine.

Sow now the battery and alternators are brand new producing good values. I also changed the belt.

I thought with this fix I found the solution for the rough idle issue. But no. The rough idle still kicks in on electrical load...
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Old 16-07-2017   #6
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

I also replaced the camshaft sensor because it was cheap and easy to replace. But it has no effect on the rough idle. Now I`m just guessing what may cause is issue.
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Old 16-07-2017   #7
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Quote Originally Posted by Ziggy122 View Post
Check the condition of the auxilary belt....

But i do wonder if the fuel pump is lacking pumping power and causes a rough idle? No idea tho
Ziggy
Yes, I replaced the belt with the new alternator but no change.

I also think about the fuel pump which could be the next thing to inspect.
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Old 16-07-2017   #8
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Quote Originally Posted by conors891 View Post
Could you monitor the battery voltage while the engine is acting up? If should be over 13V if all is good.

I would be inclined to check the voltage drop between the positive of the alternator and positive of the battery while the engine is running. Do the same for the negative. Should be a very small reading.
When the rough idle kicks in the battery fluctuates between 13.6V and 13.9V. So that looks normal when the engine slows down and speeds up by itself. I checked it with Multiecuscan.

I`m also going to check the voltage drop between the battery and alternator.
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Old 16-07-2017   #9
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

#does this engine have an idle control valve or is it a electric throttle. Sounds like a sticking ICV but I don't konow if this engine has one.

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Old 16-07-2017   #10
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Quote Originally Posted by g8rpi View Post
#does this engine have an idle control valve or is it a electric throttle. Sounds like a sticking ICV but I don't konow if this engine has one.

Robert G8RPI.
It has an ICV on the throttle body. I already cleaned and then replaced the ICV only, but that didn`t help. Then I replaced the whole throttle body with a used one (the used one also had the ICV and throttle pos. sensors) but no change.

Basically I already replaced/cleaned all the parts which were described in other topics (pre-cat O2 sensor, ICV, ignition coil, spark plugs, HT leads, battery, alternator, MAP sensor, etc...)
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Old 16-07-2017   #11
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

When I was searching the net for a possible fix about this strange rough idle issue, I found many similar videos of the MK2/2b Puntos. Which makes me think this is a common issue.

Unfortunately none of these videos describe if the problem was fixed at all.

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Old 16-07-2017   #12
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Quote Originally Posted by conors891 View Post
I would be inclined to check the voltage drop between the positive of the alternator and positive of the battery while the engine is running. Do the same for the negative. Should be a very small reading.
I did the voltage drop test but didn`t find significant voltage drop between the battery and the alternator.
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Old 16-07-2017   #13
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

This is a very weird hunting issue indeed
Ive had 2 puntos and both have done this

The only think ive never touched was the fuel system
Since there is no filter why would i?
I found no correlation between fuel and when it does it

Only electrical.load - which my belt mostly cured.....
But i still get it from time to time...

Ziggy
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Old 17-07-2017   #14
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Perhaps run 12V straight to the pump so it runs at max and see if that affects it? Faulty crank sensor or wiring issue? I'm only guessing at this stage. Next would probably be to replace the ECU and body computer.
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Re: Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Perhaps try removing the aux belt tempareraly and see how the engine runs. You could hook your car up to another car, as if you were jump starting, to keep your battery charged.
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