Technical Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

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Technical Fiat Punto mk2/2b 1.2 8v (2004) - Rough idle, mostly on electric load

Are the ECUs and body computers interchangeable between the 2 and 2b do you know?

I didn`t know that. But since I cleand / replaced almost everything that could cause rough idle I`m also starting to think this might be an ECU issue.

And also I start to think this is a common Punto 2b problem. Probably many people don`t even notice it because its severity varies.
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Does it only happen on electrical load or it's just worst on Electrical load? Is there a particular thing that seems to trigger it?

If the load on the engine increase slightly or the RPM drops suddenly, the ECU should be able to respond such that the engine rpm does not continually oscillate (it might drop once) but settles again at the correct idle revs. Given the amount of stuff you have replaced, I reckon your alternator is behaving as it should but the engine is not responding correctly. I would try replacing the crank sensor. Cam sensor is just for timing I think. The ECU gets the rpm signal off the crank sensor. Next after this would be to replace the ECU, even if just temporarily to test it.
Does it only happen on electrical load or it's just worst on Electrical load? Is there a particular thing that seems to trigger it?

I would try replacing the crank sensor. Cam sensor is just for timing I think. The ECU gets the rpm signal off the crank sensor.

The rough idle issue is intermittent. Sometimes the engine idles normally for a few days. But sometimes the idle starts to fluctuate when I stop at a red light. That`s why it is so confusing and hard to track down.

But I figured out I can force the engine to reproduce the rough idle once out of three-four times by pressing both power window switches and turning on the headlights at the same time. So i`d say it is worst on electrical load.

Today I`m going to replace the crank sensor, but after all of this I don`t really think that will change anything.
Dont bother changing crank sensor or cam sensor
If the car running and driving fine it highlights that they are working correctly.....

It leaves me thinking there is a fuel.pressure or a duff injector possibly dragging it down
Trouble is i struggle to get the fault to replicate... mines totally random
I did check my lambdas and mine were good... so i dont think lambdas are to blame....

Yes, I also replaced my lambdas. Actually my lambda was not working as it should have been, but after I replaced, it didn`t have any effect on the rough idle issue.
Dont bother changing crank sensor or cam sensor
If the car running and driving fine it highlights that they are working correctly.... It leaves me thinking there is a fuel.pressure or a duff injector possibly dragging it down
Trouble is i struggle to get the fault to replicate... mines totally random

Yes, the car runs totally fine, usually idles fine, except the random case when its idle goes mad and starts fluctuating.

But I think if it is a fuel pressure issue, then it should be a constants problem on idle and when running the car as well.

But anyway I plan to check the fuel pressure somehow myself.
Ok, I replaced the crankshaft sensor. I thought it is very unlikely that it will fix the problem, because the issue only comes up sometimes on idle. But I just wanted to be extra sure. But yes, the rough idle still comes up sometimes.
There are two more things that I can think of and what I will investigate: the ECU and the fuel pressure.

So here is the list what I have replaced and tested so far and none of these fixed the random rough idle issue:

  • MAP sensor
  • Lambda sensor
  • Ignition coils
  • Idle air control valve (IACV)
  • The whole throttle body with throttle pos. sensor and IACV
  • Injectors
  • Battery
  • Camshaft position sensor
  • Crankshaft Position Sensor
  • Alternator
  • Spark plugs
  • HT leads

  • Earth points
  • Voltage drop between battery and alternator
  • Vacuum leaks
  • ECU reset
I noticed that sometimes in the morning when I start the car the engine surges. The RPM goes up around 2000 and it never settles. I have to kick the throttle and only after that it goes down to normal.

It only occurs 1-2 times a month, but I thought it may be related to the more frequent rough idle problem.

So I connected to the car with Multiecuscan and hoped I can catch the moment when the engine surges in the morning. Fortunately I was able to catch the rare morning engine surge one time and recorded the engine data.

The data showed me that the throttle sensor indicated the throttle valve was 18 degrees open. But I didn`t even touch the throttle pedal.

I thought that I`m going to replace the whole throttle body again, although I have replaced it already with 2 two different throttle bodies from other working Puntos.

After I put on the 3rd throttle body, the engine idle sounded a bit different. Since the change - which was 2 weeks ago - the rough idle came up only once when I forced it to occur by putting on all electrical load.

So I`d say the problem is roughly fixed after replacing a surely bad lambda sensor a probably weak alternator and a throttle body.

I think the rough idle still can come up by itself sometimes, but now it occurs less frequently.


  • engine surge - RPM vs throttle angle.jpg
    engine surge - RPM vs throttle angle.jpg
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I know this is an old thread but thought I would add this to help any others with this problem. My sons punto was doing exactly the same thing as the OP so basics first plugs and leads - no change but when we were cleaning the throttle body I noticed that one of the thin wires that send signal to the coils had worn through its insulation and was occasionally shorting on the block. Chopped out the bad bit of wire re-connected problem solved!
I also hate to see problems like this but what I really hate to see is someone just changing things until he hits the "spot"

Do some diagnostics, tests, figure out the problem is instead of blindly hoping that changed part will fix the issue, like, is there any research first chief ?

Reason I get mad is I have seen so many "masters" and "pros" I drove my cart to, just blindly change parts without actually figuring out where the issue is and it pisses me off.
I work with computers and you don't see me changing RAM modules or GPU if computer wont power up.

Anyways I hope problem was fixed for all
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As this is still a hot subject, I will present a very strong solution, I struggled a little until finding it, but here it is:

The culprit is the air intake manifold gasket. It's actually gaskets, there are a set of them, individual for every cylinder plus others like MAP sensor, cooling fluid that goes to heating radiator and a couple more or so.
I had the same problem as presented here, did not change a lot of things like mikeb1, but did the testings, all good, and made sure electrical components are all good. So all good, but problem still there "totally random" as Ziggy mentioned, yet annoying a lot.

At mine, the problem, random as it was, occurring sometimes at red lights, had also a sure time of manifesting itself and I'll present it as it is a very good way of checking if that is what's causing the problem: I have a gas station very very close nearby, and on colder days or even rainy every time when I would go to put gas in, when leaving the gas station, the engine just wouldn't start normally at first key, just had to insist 2-3 times more. I was going berserk, suspected the gas station had some sort of magnetic fields interfering with ECU as it was the only place this occurred. After finding that it was the air intake manifold gasket, I realized the reason of that: the engine clearly was cold, as the first trip to the gas station was really really short, but when trying to start again, the vacuum leaks from faulty gasket permitted some condensation and the engine would not start normally, it all makes sense now. So that's the way to test it, if you have rough idle: on cold mornings start your engine and let it run a little, or even make a very short trip (200 m), then stop the car. Wait about 2-3 mins then start again and see if it starts regularly or not.
So there it is, I did this fix some time ago and that was really the culprit at mine, no problem since fixing it.
Also, I want to mention this, as Ziggy said: "The only think ive never touched was the fuel system. Since there is no filter why would i?" I did touched the fuel system and there is a filter, I suppose You can find video instructions or other post on this forum on how to clean it, just be very careful if you clean yours and you will need the special fuel pump key.
The filter was very dirty, I cleaned it good but of course, the problem was stiil there until I changed the air intake manifold gasket.
Hope this helps!
hello, I'm a new member ...
Sorry for the long speech... lol
I spent so many times on these topics, I have a Fiat Punto 1.2 8v active, it has been a super reliable car, revisions made every 10,000 in 10,000 km, since 2003 until today it currently has 173,000 km.
Moving on to what happened a few days ago, I changed the radiator and the fan, because they already had many kilometers, and I usually change one part or another for prevention, even if it is still perfectly functional, in a third dismantled the old parts and assembled the new ones, filled the radiator with liquid indicated, was waiting for the fan to fire what happened, everything ok.
The next day I go to the next city in the morning, the car arrives at the ideal operating temperature, everything is ok i think, but i notice that the idle engine goes from + -700 / 600 or less and goes back to 700 rode like this in this cycle.
That same day, connected an obd II scan via bluetooth, looked for errors, no errors, the hardware was all right, you only noticed the rotations going below and above in the obdII scan.
About three years ago I had changed the throtle body, but I didn’t put a new o-ring on it, I reused it, with this in mind I thought it must be a leak, I went to the store and bought the kit of intake joints, I dismantled the throtle body , changed the gasket, reassembled the throtle body, started the engine, and waited, until the same thing happened again ...
I went back to looking, in the intake manifold that is plastic and prone to cracking, I didn't find anything, I looked at the tubes and the ventilation valve of the fuel tank, I even changed the two o´ring of this valve, the engine did the same rpm up and down, I examined the brake assistance vacuum tube, nothing ...
With no options in sight, i examine the original throtle body, thinking about reassembling it to see if the problem would be with the hardware.
I examine the old throtle body and compare it with the new one that is assembled and I immediately notice a difference, the old one has the screw that advances or delays the degrees in the throtle almost all tangled up.
In the new one, the screw is completely unscrewed, the repair was simple, I turned on the obdII scan, I looked for a tps sensor, it was 0 degrees, I started to tighten the screw, I made a new scan, in order to raise the idle until it remained and did not sob.
When it still indicated 0 degrees and the engine at the ideal temperature was already stable, I switched on the lights and the vent in order to overload the engine and check if it could keep up with the rotation, + - 800 rpm, I gave the screw and the tps a little bit more it was indicating 0.29 degrees (it is less than 1 degree the ideal is to keep 0 degrees), but as it is I think there will be no problem.
It stayed that way and so far it has never been a problem.
What I think happened was when I assembled the new throtle body, I never adjusted anything I installed and the ECU took care of the rest, with time the screw may have unscrewed a little while it took time for this problem to happen.
Put some loctite in the screw.

I hope this help.
Hello Manni
You did not fix your problem, you just covered it up.
When rev goes down at idle, under what it's supposed to stay, it is not due to vacuum leak. Vacuum leak makes rev to go up to about 2000RPM and then down again.
The problem when rev goes under 600 RPM is the pressure being to high inside the cooling system. You even done work there before it happened, so there it is. A simple to fix cause is the valve on top of radiator cap being stuck so it does not open to release pressure when it is too high. Another possible cause is the radiator fan, it has a thermic resistence that makes it work on 1st step. If that resistance is damaged, the fan will work only on 2nd step but that means it starts to work only after the pressure inside the cooling system is too high, way too high.
I can recommend you to do a cleaning of the cooling system and a very good way to do it is the one I've posted here:
Hello Mike, iḿ going to try to explain.
My car was bought new, i am the only owner, i never mixed coolant, always used the same type, the soufage radiator is operational as new, it heats up very well, if i open the valve in the summer, even helps to cool the radiator engine ... lol
This car never have two operating speeds, it only has a full speed, the fan have just two pins one + and other - , and no termosensor built in fan or in frame, just have the temperature sensor next to the inlet mannifold, it does not have AC, and the temperature on the manometer has always indicated the same point since I bought it.
Now your explanation made me think that maybe I’ll have to see the radiator cap, it’s better to buy a new one.
Just yesterday I set up the obd scan and I was watching the rpm and degrees of the tps, they went down to 750 and the tps is now 0.
I turn on the lights and activate the soufage fan and the rpm decreases almost nothing.
And the engine doesn't go up and down, it's ok with me.
In the near future I am thinking of removing the radiator from the passenger compartment, replacing it with an electrical system, opel tigra or something.

Thank you for the advice

Vida forte e jovem