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Re: 156 wonky idle - THE FIX !!!!

I'm getting a P0500 speed sensor error lately. I erased it with Alfadiag but it came back a few days later. Does it point to the wheel ABS sensors or speedo? Could this be related to the fact that I cut that spedo wire?

The people who also cut the wire, do you have this error?
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Re: 156 wonky idle - THE FIX !!!!

I have speed sensor error as well, I did cut the wire but have now put a scotch block back for connection but speed sensor error remains!
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Re: 156 wonky idle - THE FIX !!!!

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Originally Posted by sa155ae View Post
I have speed sensor error as well, I did cut the wire but have now put a scotch block back for connection but speed sensor error remains!

So it could be related? But then you connect the wire back and the error still there?

Anyone else?
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I had the speedo error also.

I replaced the ABS central unit with another one and reconnected the wire. After a reset the error is gone.

- No more wonky idle at all
- No more little bounce with air con turned on
- No more jerky movements when taking the feet off the gas pedal

Itīs like a new car, much more comfortable and easy to drive.

It is an rather drastic and somewhat expensive solution, but definetly worth it.
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Re: 156 wonky idle - THE FIX !!!!

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Originally Posted by hsegal View Post
I had the speedo error also.

I replaced the ABS central unit with another one and reconnected the wire. After a reset the error is gone.

- No more wonky idle at all
- No more little bounce with air con turned on
- No more jerky movements when taking the feet off the gas pedal

Itīs like a new car, much more comfortable and easy to drive.

It is an rather drastic and somewhat expensive solution, but definetly worth it.
What did you connect alfa diag and have speed sensor error code P0500 then changed abs central unit and problem went!
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Re: 156 wonky idle - THE FIX !!!!

This is really interesting, it's the one thing I haven't tried!-
Anybody else prepared to take the plunge and change the ABS unit and see if it fixes the bounce?
I guess if you're happy with the cut wire fix you don't need to, but in my case cutting the wire makes it worse, I get the car speed error in Alfadiag, and due to the speed signal not being there, the ecu generates a 'fixed' speed of its own of about 20kmh, which means that it bounces all the time even when not moving, plus you get the jerky throttle cut-off, which is what that speed signal to the ecu is there for in the first place.
I've checked that with Derek from Alfadiag and it's what is 'expected' if you cut the wire (though the result may be worse on a Selespeed).

How much did the new ABS unit cost you hsegal?
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Re: 156 wonky idle - THE FIX !!!!

my MY2000 1.8 156 idles up to 2000rpm for about 20 seconds when i stop then goes back to normal - why??
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Re: 156 wonky idle - THE FIX !!!!

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Originally Posted by hsegal View Post
I had the speedo error also.

I replaced the ABS central unit with another one and reconnected the wire. After a reset the error is gone.

- No more wonky idle at all
- No more little bounce with air con turned on
- No more jerky movements when taking the feet off the gas pedal

Itīs like a new car, much more comfortable and easy to drive.

It is an rather drastic and somewhat expensive solution, but definetly worth it.
I heard about similar cases, but I also have a friend who has replaced the ABS unit recently and his bouncing is still there anyway (he never cut the wire)...

I was also getting the speed error so I decided to install a switch so I can easily change from cut/not cut and experiment both situations.

In my car it's way better in the cut position, no bouncing and no jerky either. Will check if the error has returned in a few days.
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Re: 156 wonky idle - THE FIX !!!!

Hmm, so the mystery goes on...

I have a switch on mine as well, but what happens is, in the 'cut' position, the car drives perfectly if you start it and don't go above a certain speed, but above a certain speed (50 ish) the ecu speed error suddenly appears (I can see that on alfa diag whilst driving) and then I get the bouncing all the time, even when I stop. I then have to turn ignition off and it clears the error again.
I think this behaviour is specific to Selespeed which has ME3.1 ecu though.
For that brief period whilst the error is not there, I get bounce-free idle... but I do get the slightly jerky throttle (I could live with that though if only the bounce was permanently fixed)/
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Re: 156 wonky idle - THE FIX !!!!

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Originally Posted by Alfa-BR View Post
I heard about similar cases, but I also have a friend who has replaced the ABS unit recently and his bouncing is still there anyway (he never cut the wire)...

I was also getting the speed error so I decided to install a switch so I can easily change from cut/not cut and experiment both situations.

In my car it's way better in the cut position, no bouncing and no jerky either. Will check if the error has returned in a few days.
I just did a switch like you because sometimes I get smooth idle and other times when cold I have yo yo idle and jerks. I cant afford all these things at the moment TPS, MAF, ARB, speed sensor it really needs a good few hundred quid spent.
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Re: 156 wonky idle - THE FIX !!!!

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Originally Posted by DAL-FA 156 View Post
my MY2000 1.8 156 idles up to 2000rpm for about 20 seconds when i stop then goes back to normal - why??
very common problem, its usually the idle speed controller on the throttle body. easy job, and cheap if you get a scrapyard part.
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Re: 156 wonky idle - THE FIX !!!!

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I just did a switch like you because sometimes I get smooth idle and other times when cold I have yo yo idle and jerks. I cant afford all these things at the moment TPS, MAF, ARB, speed sensor it really needs a good few hundred quid spent.

I know...if we could only know FOR SURE what to replace! At least the money would be weel spent.

I've heard stories of people that replaced the idle actuator and it didn't fix. Now I know someone who replaced the ABS unit and it didn't fix it either...

Andy, mine is a M1.5.5, so I guess that's why I don't get the same symptom after cutting the wire?
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Re: 156 wonky idle - THE FIX !!!!

I had the same issue with my 156ts. It idles between 500 and 1500 rpm yet some days it wouldnt do it at all. It would generally do it when the engine got up to temp. I cleaned out the throttle, i cleaned the MAF as explained. Nothing worked. The car would cut out if i came to abbrupt stop or turned too quick in an intersection. I drove me insane!

My solution... Bought a new MAF, installed it. Reset the ECU, drove the hell out of it. AND BINGO!! Not only is the car idling the way it should, it also has increased the power output, waiting to see what it does on the dyno.

Thanks to everyone on this forum for there tips. It really helped me!

Take care
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Re: 156 wonky idle - THE FIX !!!!

I'm gonna try changing Maf next as the power loss is stupid, I seem to be losing loads of BHP.
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Hi, I hope that no one is mad because I opened a semi-dead thread.

Firstly, I read through this whole thread, all 7 pages off it.
Secondly, the problem I am experiencing is similar, but not exactly the same.

For a good description, please see the thread I started here:

http://www.alfaowner.com/Forum/alfa-...e-shudder.html

But in short, my problem is when slowing down to stop car, as soon as the revs hit idle speed when I clutch, the revs go down to about 400 RPM, then back up to about 1000 RPM, repeats this cycle about 2 times, then return back to "normal" idle at 900 RPM.

This first started happening about a few days ago, after I got my car back from repairs at the service centre. It wouldnt start. After replacing the Crank\RPM sensor, they found a dead/loose connection wire close to the ECU, which was the actual problem.

So the difference between the problem described here and mine is that my engine doesnt die, or jerk. And the problem is only with idle. Driving otherwise no problems at all. Also when just leaving the car to idle at standstill, it is idleing nicely at 900 RPM. So its only when slowing down and clutching, but I also get the problem when just revving in neutral. So it seems like its battling to get to the right idle RPM ONLY coming down from higher revs, and it does not do this when the car is cold. But 2 minutes driving sure as hell it happens.

Here is what I have done:

1. Reset ECU by dcing battery for more than 45 mins, starting an idling for 15 mins.
2. Resetting the idle (90 secs on and off trick)

So I suspect the idle motor, MAF sensor or the lambda sensor to be faulty. I am also considering cutting that wire behind the speedo. Though I would prefer to spend money to replace whatever is the real cause, even if it costs more, as long as I dont have to take the car to the dealers.

O car is a year 2000 model 156 2.0 TS.

I hope with all that detail someone can help me narrow down the problem.
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Originally Posted by aLiAz View Post
Hi, I hope that no one is mad because I opened a semi-dead thread.

Firstly, I read through this whole thread, all 7 pages off it.
Secondly, the problem I am experiencing is similar, but not exactly the same.

For a good description, please see the thread I started here:

http://www.alfaowner.com/Forum/alfa-...e-shudder.html

But in short, my problem is when slowing down to stop car, as soon as the revs hit idle speed when I clutch, the revs go down to about 400 RPM, then back up to about 1000 RPM, repeats this cycle about 2 times, then return back to "normal" idle at 900 RPM.

This first started happening about a few days ago, after I got my car back from repairs at the service centre. It wouldnt start. After replacing the Crank\RPM sensor, they found a dead/loose connection wire close to the ECU, which was the actual problem.

So the difference between the problem described here and mine is that my engine doesnt die, or jerk. And the problem is only with idle. Driving otherwise no problems at all. Also when just leaving the car to idle at standstill, it is idleing nicely at 900 RPM. So its only when slowing down and clutching, but I also get the problem when just revving in neutral. So it seems like its battling to get to the right idle RPM ONLY coming down from higher revs, and it does not do this when the car is cold. But 2 minutes driving sure as hell it happens.

Here is what I have done:

1. Reset ECU by dcing battery for more than 45 mins, starting an idling for 15 mins.
2. Resetting the idle (90 secs on and off trick)

So I suspect the idle motor, MAF sensor or the lambda sensor to be faulty. I am also considering cutting that wire behind the speedo. Though I would prefer to spend money to replace whatever is the real cause, even if it costs more, as long as I dont have to take the car to the dealers.

O car is a year 2000 model 156 2.0 TS.

I hope with all that detail someone can help me narrow down the problem.
My idle bouncing only happens when the car is moving and I clutch it, like aproaching a stop. The revs will drop to 500 then go to 1500 and then drop to 500 again and so on. When the car stops moving the idle bouncing also stops completely and stays at 900. The engine never stalls. I have replaced lots of things: MAF, camblet, variator, plugs, cleanned TB and injectors, etc. Other than that the car runs just great, very fast and no dead spots.

I'm now considering replacing or having the ABS unit checked and fixed, as my garage always suspected that would be the culprit.
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That free hour long Saturday morning surgery with Autolusso sounds good, maybe they could find the problem!
You have to book in advance.
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Could you just help with this folks!

Does this 'cutting the wire' work on the GTV - same solution to the idle problems???

Thanks
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Mine only does it when slowing down and clutching so I would assume the abs ECU circuit is involved. I also have had a new idle actuator and didn't solve the problem.
I aim to change maf next and if that don't cure it I may take the plunge and change the ABS ECU unit as I have a spare in shed I just hope its the same type as it was off an imported car.
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Hello..
My car does the idle issue while moving, but there is a difference: Mine does not have a ABS unit! So, the question is: Is the ABS sistem really involved ? I agree that the ecu wants to know if the car is moving or not and this signal is sent by the speedometer, so, cuting the wire the ecu thinks the car is always stoped masking the problem, as we already know. No one has really thought in having a closer look at the speedo ? How is this signal? Has anyone used a osciloscope on that wire ? It is probably a noise problem and maybe a simple LC filter could fix it ?

So, who want to watch the signal in a osciloscope and tell us how it is ? I have no acces to a osciloscope.
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I do suspect a noise in the signal could be responsible for this issue. How can I make a LC filter? I don't have an osciloscope but I could centainly try the filter solution.
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Alfa-BR

Dear Alfa-BR.
In order to make an apropriated noise filter we must understand how is the signal. If the signal is a simple logic high or logic low, the filter is simpler, also, a filter would decrease the response time of the signal, there are many items to be studied and the first step is to understand how is this signal. That's why we need an osciloscope.

PS: I gess u're Brazilian, I am Brazilian too, and I have a feeling we two belong to the Alfa Romeo BR club... my name is Felipe de Andrade Neves Lavratti.
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I've just been reading through this thread out of interest; I guess from the sound of it, the only downside to cutting this wire is that if you're trying to stop on a surface with very little grip, the ABS may make it very difficult (ie: it isn't disabled at very low speed to enable you to actually stop). Very few occasions in the real world where this scenario would cause a problem IMO.
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Hi again folks, been monitoring this for a while, but in response to a question from Fanl,
I have some info to share:

First of all some facts as I know them (I'm pretty sure about this as Ive spent a long time looking at the circuit diagrams and am an electronics engineer, but if anyone disagrees feel free to question this):

- On the 156 the speed signal comes from the 4 wheel sensors and goes directly to the ABS ecu.
- the ABS ecu uses this signal directly to deal with its braking requirements, so there is NO affect on the ABS braking performance caused by cutting any wires coming out of the speedo. The ABS is self contained in this respect.
- the ABS unit then sends a single speed signal to the Speedometer, which uses it to display the speed
- The speedo then sends 3 (buffered) copies of this ABS-derived speed signal out to the following places:

a) the engine ecu. This is the famous wire that we are discussing cutting on this thread. The purpose of this signal is to allow the ecu to eliminate a jerky fuel cutoff when you take your foot of the accelerator and the car is moving at speeds above 20kmh. When it knows the car is going at this speed it switches on a special servo that lets the engine rpm die down more slowly. The problem we are all having is something to do with this system not working properly! The big question is -how, why, what changes to make this happen?

b) the aircon control ecu - this needs a speed signal to compensate for the amount of air entering the car when travellling at speed, I don't know exactly how this works, I imagine its only related if you use the 'auto' setting which I never do...

c) the Selespeed ecu on Selespeed cars... this is used to determine when to automatically change down gears when the car is slowing down.

The reason there are three copies is just to prevent a fault or short cct in one unit from affecting the signal to the others. Although none of these signals performs a safety-critical function.


Next fact: I have measured the output of the speedometer speed signal on the wire from the Speedo that goes to the engine ecu (I assume all 3 of these signals are the same, but this is the one we are concerned with). I wanted to see if there was any noise on the signal that might explain the idle bounce, or perhaps a strange behaviour at the lower speed values. Unfortunately, there was no noise on the signal, and it behaves in a linear fashion as you would expect.
Here are the details of how it is formatted:

Square wave 0 to +12V.
(Car stopped -speed zero - I think it sits a +12V)

Frequencies:

0mph: 0Hz
minimum rolling along at <1mph: 1.8Hz
~5mph: 6Hz
10mph: 16.6Hz
20mph: 32Hz
30mph: 42Hz
40mph: 62Hz


One way to solve this problem would be to build a circuit that can be inserted in the speed line to the engine ecu and will monitor the frequency of the signal and cut off the output when the frequency falls below an adjustable preset threshold (eg 5-10Hz).

This would still only be working around the problem, we still don't understand what it is that changes in the engine over time that makes this idle bounce happen... but I think it's a design error in the ecu software that the designers didn't take account of how the engine response to fuel cutoff changes as the engine wears, and whilst there are a lot of ways in which the ecu does deal with parameters that change with ageing components, this is one that they got wrong...
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Quote:
Originally Posted by Alfa-BR View Post
My idle bouncing only happens when the car is moving and I clutch it, like aproaching a stop. The revs will drop to 500 then go to 1500 and then drop to 500 again and so on. When the car stops moving the idle bouncing also stops completely and stays at 900. The engine never stalls. I have replaced lots of things: MAF, camblet, variator, plugs, cleanned TB and injectors, etc. Other than that the car runs just great, very fast and no dead spots.

I'm now considering replacing or having the ABS unit checked and fixed, as my garage always suspected that would be the culprit.
I cured my dodgy idle quite simply with AlfaDiag .. on the older cable-throttle cars you can reset the idle actuator (the black box on the throttle). Do this followed by an idle reset (90 secs trick) and you may find it is OK. It may also help to remove the actuator, and replace it holding the throttle butterfly closed. This will "force" the gearing in the actuator to turn back to the correct position. But do this gently or you could damage the nylon gearing inside.

I thought part of the problem was the need to pull the throttle open to remove the throttle cable when I removed the body to clean it. So I now remove the actuator unit BEFORE I take the cable off and replace it after replacing the cable as you have to turn the butterfly to unhook it from the cam. It can be a bit fiddly with only two hands but it isn't impossible.

When the actuator is moved from the correct position, I think the signal from the ECU tries to open & shut it at the wrong time which causes the idle drop. It can also manifest itself in jerking as you "Feather" the throttle in traffic on negotiating roundabouts, which isn't pleasant. I'm no electronics engineer, but having played with a couple of throttle bodies, only resetting the actuator had the desired effect.

In extreme cases you may need a new actuator especially if you (or a previous owner) have been over enthusiastic with the throttle body when cleaning or manually opening and closing the throttle by hand.

cheers, Gary

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