Technical Engine revs at 2000 RPM on idle

[Mike1alike]

RalphM Yes, it is. The throttle butterfly works good, the same does it's position sensor.
judderbar This is what I suspect the most to be the cause of the problem, the cooling system. There was no presure inside, after the engine was running. Then I've put the new cap and for the first time something worked different and the problem was gone, even if just for a ride or 2. Then today, when I've put water in (insted of coolant, just to wash the system, I will put coolant soon) at the begining engine ran nice. And those pieces that came out (by the way there is pressure now, so the water pump is working and the engine does not overheat at all) made me think there might be more of that and it's like the pump admision is somehow clogged and in that way, sending water to the circuit but not having on the intake the necessary amount, it could create air pokets. And I'm thinking that the sensor cannot read temperature when air is on the sensor insted of coolant and happens this problem, the one you've experienced due to the lower temperature registred by the sensor (just as in cold start) the computer gives the signal to rev up a little. And then, when coolant comes again, the signal is the one for correct rev on hot engines. So the air pokets come in waves and this creats the surging.
I would have thought that by purging the system, whatever is clogging it would come out. Or maybe I just didn't bled it good, I will try again tomorrow.
If I bleed it and the problem is still there, I' m thinking I will try to put some pressured water inside the engine, by a hose connected somewhere up from where to push down onto water pump and have the radiator hose open so that if something is there, to get it out.
The thermostat would be a good place for that, but the cold water will close it so that's not good. I think a line from the short circuit should work. If you can recommand me the best place to insert the water in the cold engine, please tell.

 

[Mike1alike]

I have found this Punto Mk1 thread whith the exact idle high rev problem (among other problems)
https://www.fiatforum.com/punto/298002-mk1-punto-idle-revving-high-idle.html
There it seems to me that replacing the O2 sensor was the fix. What do you reckon, have I missed something, is anything else that did the trick?
I will test my O2 sensors and will compare the results with previous recordings when I did not have this problem. Also, I will check the exhaust manifold, hope it isn't cracked.

 

[Mike1alike]

I've tested the O2 sensors and it does look like this is where the problem comes.
It's no need to compare the results with previous recording, as I've managed to record the readings now both when engine runs OK and whet it does not. At first start, until the first press of the acceleration pedal, the idle is perfect, around 750 RPM.
My interpretation is that the pre cat sensor is the faulty one and then the after cat just drops because of the first one. And it shows clearly that the first drop of the signal to zero comes from the pre cat sensor and it is known to have a bigger impact on the air/fuel ratio mix.
What do you think?

 

[Mike1alike]

I've cleaned the pre cat sensor, but with no effect.
Do you think that it is possible the sensor to be good and the problem to be the petrol? The problem just started on the last tank refill, that is why I'm asking and I find very strange this sensor's voltage, it has moments when it works and moments when it cuts off. Is the sensor broken and it just needs replacement? Is this the correct sensor that I've focused on, or is something wrong with the other sensor. I will change them between them, to see if something goes different. I really wouldn't want to buy something else that will not fix the problem.

 

[Mike1alike]

And another thing that bugs me and makes me wonder if any of the O2 sensors is broken, is the fact that they store no error and the check engine light doesn't light up.

 

[Mike1alike]

Well, I could not test if the pre cat O2 sensor is not working right. I tried to put the after cat one in its place, but that one is stucked. I've managed to make it move a little bit, but that's all, it doesn't come off and does not rotate anymore to any direction. And the exhaust line after the flexibile part cracked again, I've had it repaired some time ago.
The revving high on idle problem is still present.
No one answered me, do you believe that the temperature sensor could be at fault, even if it shows accurate temperature both on the diagnose reading and on the dash board?

 

[Mike1alike]

I have started the engine with the pre cat O2 sensor disconnected and it does exactly the same. So I would rule that out, the O2 sensor it's not causing this problem.
I think next I am going to replace that temperature sensor. I have seen the engine acting like this while I've changed the coolant and during the topping up and bleeding. So it seems to me that that sensor can give this effect. But it confuses me that it shows good numbers.

 

[Mike1alike]

Now I've started the engine with the temperature sensor disconnected and for sure there is a difference. It still revved up, but in a different mannor. Did not pass the 2000 RPM and it was not so quickly up and down, not surged. When it went up, it stayed there for a while, like when you start cold and it's very cold outside. And then, it even had more moments than before, when it dropped down to normal idle. It still had at a point then some kind of a surge, but only between 1400-2000 and without quik changes. I really don't know. I will try a new sensor, but I don't have very much trust that it will solve it.

 

[judderbar]

Now I've started the engine with the temperature sensor disconnected and for sure there is a difference. It still revved up, but in a different mannor. Did not pass the 2000 RPM and it was not so quickly up and down, not surged. When it went up, it stayed there for a while, like when you start cold and it's very cold outside. And then, it even had more moments than before, when it dropped down to normal idle. It still had at a point then some kind of a surge, but only between 1400-2000 and without quik changes. I really don't know. I will try a new sensor, but I don't have very much trust that it will solve it.

I think you need to make sure you dont have an air leak somewhere or the throttle is not working correctly. You could remove the throttle body and just have a small opening for testing. A cigarette can be used as a smoke generator. Not likely to be the temperature sensor if you get those crazy revs with it disconnected.

 

[Mike1alike]

Yes, that's another thing that I've though too, to test for vacuum leak with cigarette smoke. I will do that. And the throttle is working correctly for sur. And the same for TPS. The throttle is opening by cable it's not stucked anywhere and it opens and closes as it should.
To do the smoke test I don't think I need to remove the TB, I'll just close the step motor opening and to blow smoke in I'll open the butterfly.
But I've read reports on VW Golf with the exact same issue that was fixed by replacing the temperature sensor, so I'm not disconsidering that. I've let myself misquided by the readings of temperature. But I think that If I'd mesure the sensor with an oscilloscope there could be seen droppings of signal. I don't have an oscilloscope though, so I will replace the sensor.

 

[Mike1alike]

I did the cigarette smoke test and shows no leak. I've inserted a hose through the TB and isolated with a cloth the area, blew smoke through the hose and couldn't see smoke coming out anywhere. After that, I've open the butterfly and smoke came out. I now it would be a certain test if I'd had a way and a tool to insert the smoke under high pressure, so the test I've performed is just informative, although, by the preaty large quantity of smoke coming out when I've open the butterfly, it points to "no leak" situation. If there is a leake, it is a very thin crack that opens up when the engine is hot. But considering that I have sprayed carbon cleaner in the area with the hot engine running and during the time it revved itself, for now I'll put that as "no vacuum leak".
I've ordered a new temperature sensore, I really hope that to be the fix.

 

[Mike1alike]

Unfortunately, there's absolutely no improvement whatsoever even with the new temperature sensore. And this time I've spent a little bit longer doing the air bleeding. There is a little weird thing though: even after the bleeding it seems to me that the heater does not quite give so much heat as it should give. At this outside temperatures (it's about 38C) the heat should be really hot, coming from the heater. And some other details: like the first time the other days, when I've topped up the cooling system with water, there went 5l in. First time I've thought I must have spilled some while topping up, but it's kind of much. The system's capacity is 4.2l. And the water, just as antifreeze before, is full of rust residue. The first one was full, this second one looks already rusty.
So I'm thinking maybe there's some problem like a hole in an iron pipe from the cooling system. I think that if would be a problem with the HG or the HG seal (wich I've replaced in 2018), the engine would not have moments of running very nice, as it has now, and this rev up would not quite happen.
What is eye catching is that O2s test where their signal drop to zero. Could it be an interrupted cable or maybe an ECU problem, a loose contact or something broken inside the module?
You guys have any other ideas, recomandations?

 

[Mike1alike]

I think I have reached to what's causing the problem: IACV. It really is the one making all this, seeing it open in FiatEcuScan I thought that ECU is signalising it to open so much. But in reality I think that it just gets stucked open, therefore the high rev situation, ECU injecting more fuel, to balance the air/fuel ratio. For now, after I started the engine and idle settled to about 750 RPM, I have disconnected the IACV's cable and took the car for a ride. No high idle whatsoever, it ran very smooth. Of course now, there is a very slight chance that IACV was given a signal to open up more and not being connected it couldn't open now, but I think there's very little chance of that and if it would be, it would be the worst case scenario. I'm almost certain that IACV just remained stucked open and sometimes is would get loose and close, therefore that erratic behaviour, with moments of nice idling and others with high rev.
I've took the TB down now, I cannot get the IACV out of it and I'm not forcing it. If cleaning it on the TB dosen't solve the issue, I'll insist on getting it down and maybe replace it with a new one. I've cleaned it with carb cleaner and Q-tips and after that I've closed the "mouth" of TB with a bag and rubber band, reversed the TB and I've put petrol onto the IACV and let it to soak.

 

[judderbar]

I think I have reached to what's causing the problem: IACV. It really is the one making all this, seeing it open in FiatEcuScan I thought that ECU is signalising it to open so much. But in reality I think that it just gets stucked open, therefore the high rev situation, ECU injecting more fuel, to balance the air/fuel ratio. For now, after I started the engine and idle settled to about 750 RPM, I have disconnected the IACV's cable and took the car for a ride. No high idle whatsoever, it ran very smooth. Of course now, there is a very slight chance that IACV was given a signal to open up more and not being connected it couldn't open now, but I think there's very little chance of that and if it would be, it would be the worst case scenario. I'm almost certain that IACV just remained stucked open and sometimes is would get loose and close, therefore that erratic behaviour, with moments of nice idling and others with high rev.
I've took the TB down now, I cannot get the IACV out of it and I'm not forcing it. If cleaning it on the TB dosen't solve the issue, I'll insist on getting it down and maybe replace it with a new one. I've cleaned it with carb cleaner and Q-tips and after that I've closed the "mouth" of TB with a bag and rubber band, reversed the TB and I've put petrol onto the IACV and let it to soak.

IACV - we call that here the idle control valve. Another thread here this week about removing that. Suggestion is to put a jubillee clip on it (radiator steel clamp) and then lever on the clip against the throttle body with a screwdriver

But your cooling systems consumption of water and the stuff on the radiator cap and the poor heater in summer are pointing to something that does not sound very good at all.

 

[Mike1alike]

Yes, the idle air control valve. I did get it out today, as there is no fix with just cleaning it. Ordered a new one, I'll have it tomorrow.
I know what you're saying about something bad, I've thought of that myself, it's either the HG or HG gasket, right? I hope they are ok though, as the temperature did not rise at any point above normal. And if there would be something wrong there, I don't think that the engine would rev up like it does and in the same time to have moments when it runs just fine, even after it is hot.
I will put the new idle control valve tomorrow and see it from there. I really hope that it will be the fix, though.

 

[Mike1alike]

Yeap, there is definitely a problem with the cooling system, the water is very low again, so air pockets must be also. For now I've also ordered the coolant water pipe, the metal one that feeds the water pump from radiator and has also the return ramification for the short circuit (when thermostat is close). It being the only iron pipe and considering the amount of rust in the coolant and 2 waters, seems a good idea to replace it. And this is how it looks like on the outside (not good at all).

 

[Mike1alike]

Good news, very good news! I have fixed it.
The idle contol valve was making all this havoc, repeatedly high rev on idle and also accelerating by itself while driving.
First I've replaced the cooler pipe and it looks like the rust was coming from the old pipe, now the water is clear. I'll put antifreeze tomorrow. After this, I've tried the engine with the old idle control valve and it still revved by itself. Then I've replaced the ICV and it runs great.
And there were no leaks from the cooling system, the water was towards min because I opened up the cap once while engine was running and some water spilled out.
And a little detail about the pipe, the old one's gasket was made of 2 rubber layers with a metal bushing in between them. I got the inside rubber gasket out and felt that there is more inside. I though that it is stucked from heat and bothered a little to get it out. I I really gave the tips of my fingers a "treatment". Then I've noticed the bushing and pushed it inside of it's own so I can get it out.
This in the picture is the rusty old pipe and the gasket.
And this is the code for the pipe: 55245749
and this is how it looks like, the gasket it's thicker and fits nice, no bushing needed
https://www.google.com/search?ie=UT...88+Bravo+Stilo+Idea+Grande+Punto+199+55245749

 

[Mike1alike]

This is the code for IACV that I've bought and replaced.
The engine works great after that replacement, so that was the cause.

 

[Razvanstanescu]

I have the exact same issue with a Fiat panda I bought, hole in radiator and it was reving 1500-2000 rpm continously. Replaced radiator - same, cleaned throttle body - same or worst, replaced throttle body was ok for a min until accelerate then again now stays at 2k rpm and fluctuates less

At this point after seeing this thread looks pointless to swap anymore parts

Thank you

 

[Mike1alike]

That could be caused by a vacuum leak (technically that was at mine too, but there the leak was happening through the IACV, which didn't close enough when it should, being broke). So, first thing, check the breather, the one in the pic below.
Also, under the throttle body, between it and the intake air manifold, there is a gasket and it is another possible vacuum leaking point. I think you can buy that gasket on a set containing all the gaskets that are on the manifold, including the 4 very important that fit between manifold and Cylinder head.
I have a picture of that gaskets set, don't know if is the same on your Panda, but it could be, check it.

L.E. I remembered that when I had the broken IACV, the idle didn't fluctuate just between 1500-2000 RPM, it also dropped below 750, to like 500 RPM. That is a detail for a bad IACV. When idle is only above normal range, it's vacuum leak.