156 wonky idle - THE FIX !!!!

if it worked for you guys, i'll give it a try (Figures Crossed)

i had the same problem exactly but fitted a new idle switch and its fine now , i wouldn,t feel happy cutting pins off ecu board i must admit but if its sorted you out , fair play ...

Originally Posted by Pete McK

If you're having a go, it's the green/white wire from the larger of the two plugs on the speedo back:

pin 15 on mine was green/black pin 16 was green/white

rob.

I will try the lamba sensor first. Since my car smell very bad. will update how my car go next week.

I have been reading this thread with interest. For the people who have cut the wire, how is the car running now ?

Cheers

i was the first to do it and my car has not had a problem with the idle since, or anything else related to it.
it is a fix for a specific problem and not a cure all, if the idle bounces while the car is stationery then its something else.

Mine has never run better since I snipped it

What is that wire which many has cut off, some kind of abs-wire? Is it possible the problem locates in some abs-sensor or pump? Where this wire comes and what is its task?

Originally Posted by jarama

What is that wire which many has cut off, some kind of abs-wire? Is it possible the problem locates in some abs-sensor or pump? Where this wire comes and what is its task?

The speedo takes its signal from the ABS, from the speedo the signal is repeated to the climate control and to the ECU. I am guessing the signal to the ECU is telling it the car is still moving so keep the idle slightly higher than when stationery, this seems to be the problem it cant keep it high.
If you read the thread from the start you will know as much as we do, i have not met anybody on here who can explain it but it works with no side effects that i have found.
Several people on here have managed to fix the problem by replacing different parts and thats great for them, this seems to be a fix for those who have tried all those things and got nowhere, so the debate goes on cut it or not cut it, the wire and the choice is yours.

Have fun

I cut mine, as with others I can confirm no side effects. Fixed the problems.

I gave another ttry today as I'm sick and tired of the bouncing (only when moving). I removed the ABS 60A fuse but it didn't help. One thing I didn't understand, Maverick, the speedo continued to work even with the fuse removed?

I think it's temp related as it's much worse when the engine is cold and tends to disapear once it's warmed up.

if the speedo continued to work then its not disabled. A sure way to do it is to disconnect the sensors, 2 at the front next to the suspension towers an 2 at the back behind the wheel arches under the carpet. Removal of the 60amp fuse was somebody elses spin on it, i removed 2 fuses from under the steering column after looking in the handbook to find which ones, but disconnecting sensors is easy and you cant get the wrong ones.

Originally Posted by Alfa-BR

I gave another ttry today as I'm sick and tired of the bouncing (only when moving). I removed the ABS 60A fuse but it didn't help. One thing I didn't understand, Maverick, the speedo continued to work even with the fuse removed?

I think it's temp related as it's much worse when the engine is cold and tends to disapear once it's warmed up.

Removing the fuse made no difference to mine, but snipping the wire sorted the bouncy idle. My probs were temp related too, when temp is at 70 (warm) being the worst.

Not that I'm that bothered anymore but because my idle prob use to vanish if I revved the car past 4k first (but would return in 30 secs) I wonder if its either a) fuel pressure related or b) voltage related. Either way I'm glad its fixed as I was about to torch the blo*dy car!

Originally Posted by Maverick

if the speedo continued to work then its not disabled. A sure way to do it is to disconnect the sensors, 2 at the front next to the suspension towers an 2 at the back behind the wheel arches under the carpet. Removal of the 60amp fuse was somebody elses spin on it, i removed 2 fuses from under the steering column after looking in the handbook to find which ones, but disconnecting sensors is easy and you cant get the wrong ones.

Thanks Maverick. I'll try to remove the fuses under the dash, how many? I still think in my case it's related to temp. I've changed the temp sensor recently but it didn't fix it. Maybe a new stat?

Did you reset the ECU after removing the ABS sensors? Or did it stop bouncing imediately?

Cant remember which fuses i just looked in handbook, to disable it properly you need the ABS light to stay on and also the HANDBRAKE light to stay on which lets you know EBD is disabled, i found it easier while working this out to disconnect the ABS sensor plugs. Dont think i did an ecu reset but at the time it was on AlfaDiag a lot so it is possible.

You may be right about the temp you just never know, what i do know is mine was ok until it was upto temp and then it would start.

Before I cut mine, when I started it first thing in the morning there was no bouncing until about 500 yards, then after it warmed up I'd get the bounce

hi all

i think i may have some problem related to bouncing idle, or there again mayb not. The problem i have is that when engine cold i drivr off car jerks and slows down abit until u put ur foot down then ok. It will do this for some time until engine waarm then evrything Ok. Also sometimes i change from 1st to 2nd gear no probs and sometimes the car just slows down and then shoots off . Mine is an 2.0ts selespeed year 2000 so would the wire fix , cure my prob or is mine something else, i have changed Lamda and Maf just recently within last 6 months and also had my cam belt, idle and tensioner belt along with cam variator done. But still the same old scenario. Once warm evrything OK only when cold.

any help appreciated.

Thanks
Eggie

Hey guys, this is my first post on this forum, I saw a link to this thread on the Alfa156.net tech forum, and since I have also been suffering with this problem on my Selespeed for several years, I think it's a major step forward in the search for the <complete> solution for this problem...

As a bit of an electronics specialist I have some thoughts on this - first of all congratulations to Maverik for coming up with the idea to cut the wire in the first place. I think this proves that the problem is electrical. I think there is more to it though. The reason I think that is that on my car it did not fix the problem completely, but had a very interesting side effect.

my theory on what is the reason for the ecu to be fed with the speed signal from the ABS is that when the car is moving it invokes a special way of cutting off the fuel more gently than when the car is stopped, this is to avoid a 'jerky' feel when you take your foot off the gas when moving. On my car, cutting the wire from the speedo to the ecu partly fixed the bouncing idle, but also made the throttle feel more jerky when you take your foot off the gas.

What is more interesting is what happened when I looked at the car speed display in Aladiag after cutting the wire from speedo to ecu. Initially the speed was zero, as expected, but after a bit of driving, especially above a certian speed, the speed would suddenly jump up to a fixed value of about 20km/h, and stayed there even if the car wasn't moving until I switched the ignition off and then on again. When this happened, the idle bounce came back again, even when the car was stopped - again, this would be expected given what we know.
The question is, what caused the speed to give this erroneous value in the ecu, when the wire has been cut? I suspected this was because if you leave a wire which is an input signal 'floating' electrically, it can go to an undefined value that can be interpreted by the circuit (in this case the ecu speed input) as a false signal. What you normally have to do is to tie the line via a resistor, to either ground or the + rail (this is called a pull-up or pull-down resistor). So I tried this, but to my surprise the bouncing came back with a vengence, and all the time! Looking at Alfadiag, sure enough it showed a randomly generated speed signal... If i had the windscreen wipers going, it was even more crazy. I tried both pull up to 12V and pull down to earth, via a 1k resistor, and with the same result.

This indicates to me that electircal noise is getting onto this line, and being interpreted by the ecu as a speed signal, which confuses the system that is supposed to ramp the rpm down gently when the foot comes off the gas - hence the bouncing.
I think that, if this noise is there when you disconnect the wire and connect it to earth, it is probably also there even when the wire is connected to the speedo - ie, it could be there along side the real speed signal, and therefore confuse the hell out of the ecu.

The question is , where is this noise coming from? This is where I don't yet have the answers. Certainly I've listened to the pulses that are generated by the speedo signal on the cut wire and they are similar in frequency to the pulses generated by the ignition coil ccts, or the injector circuits.

One other thing I have noticed is that I started to get a lot more interference on the long wave radio band at a certain mileage, which was not there when the car was new. This did seem to correspond with the time when the bouncing idle problem started. I improved this recently by cleaning the ground connection on the aerial amplifier in the rear C pillar... but it's quite a well-known problem with many cars that all the earth connections can deteriorate over time and cause all sorts of problems. The source of that noise is still there, and we need to find it. It's bound to be a generic problem on all 156s...

I know someone on here said they'd had their earths checked, but it could be other things as well - for example the alternator... now there's an idea - disconnect the alternator and see if the problem goes away. Only problem is you have to get under the car to access it, and in this weather I don't fancy that!

Although my car is a Selespeed, I believe this particular fault has the same root cause in both the manual and the Selespeed, maybe just more sensetive on the Selespeed, as there is more load on the electrical system with this system.

So my new quest is to find out how to reduce this noise - is it a grounding problem, a noisy alternator, is it a bad connection in one of the in-line plugs, is it noise in the speedo area specifically (I'm going to check this by connecting my pull-down to a ground point nearrer to the ecu itself) - if anyone else has some ideas on this theory, lets hear them!
Ive been having a good look at the power and ground wiring on the workshop CD, and there are quite a few hidden earth points that could be removed, cleaned and tightened up. There's also the ECU itself - it's probably got an internal ground connection that could corrode, I saw this when I opened up my duff airbag ecu once.
A good way to check the effect of any improvements here is going to be to monitor the noise level on the long-wave radio.


By the way, referring to the posts above from AlfaBR and eggie: anyone with a Selespeed should NOT disable the ABS unit in order to get rid of the speed signal - there is another feed from the speedo to the Selespeed ecu which is essential and is used by the Selespeed to know when to change down gears automatically, and disabling the abs will take out all three of the speed signals (selespeed, main ecu and aircon) as well as being undesirable safety-wise. I havent tried disconnecting this line to the selespeed ecu (pin 14 I think), but the gearbox will definitely not be happy!

Sorry for the long post, I promise this is a one-off...but this has all been majorly exciting for me, and again, thanks due to Maverik for the great idea in the first place!

Originally Posted by Selespeed Andy

By the way, referring to the posts above from AlfaBR and eggie: anyone with a Selespeed should NOT disable the ABS unit in order to get rid of the speed signal - there is another feed from the speedo to the Selespeed ecu which is essential and is used by the Selespeed to know when to change down gears automatically, and disabling the abs will take out all three of the speed signals (selespeed, main ecu and aircon) as well as being undesirable safety-wise. I havent tried disconnecting this line to the selespeed ecu (pin 14 I think), but the gearbox will definitely not be happy!

Sorry for the long post, I promise this is a one-off...but this has all been majorly exciting for me, and again, thanks due to Maverik for the great idea in the first place!

Hello Andy, and WELCOME to this forum! Your help is very much appreciated! No problem at all with the loooooong post!

Very interesting thoughts! I think you're right about the reason for the ECU knowing the car is moving and to avoid the jerkiness. I heard that cars that have been remaped never had this problem again.

I agree with you, it must be electrical and it could well be noise or even bad connection. I've been discussing this problem for months with lot's of people, mechanics, 156 owners. One thing that everyone agrees is that when the car was new this never happened! So it must be related to ageing of components or something like that.

My car is not a Selespeed, so I disconnected the ABS fuse just for a few meters and it was enought to know it would not solve my problem.

Please keep up with the work, I think we're getting really close to the problem. I could try to disconnect the alternator (it's sunny and warm here in Brazil! ), any other ideas?

Originally Posted by Alfa-BR

Hello Andy, and WELCOME to this forum! Your help is very much appreciated! No problem at all with the loooooong post!

Very interesting thoughts! I think you're right about the reason for the ECU knowing the car is moving and to avoid the jerkiness. I heard that cars that have been remaped never had this problem again.

I agree with you, it must be electrical and it could well be noise or even bad connection. I've been discussing this problem for months with lot's of people, mechanics, 156 owners. One thing that everyone agrees is that when the car was new this never happened! So it must be related to ageing of components or something like that.

My car is not a Selespeed, so I disconnected the ABS fuse just for a few meters and it was enought to know it would not solve my problem.

Please keep up with the work, I think we're getting really close to the problem. I could try to disconnect the alternator (it's sunny and warm here in Brazil! ), any other ideas?

We now know that taking the fuse out is not the same as cutting the wire, I took fuse out and was the same, cutting the wire helped a lot but I dont think it's a cure.

I hope you do find the real reason for the bounce as i will find it interesting. Unfortunatly my electrical knowledge will allow me to fit a plug and luckily follow a wiring diagram.

looking forward to the full blown cure.

Hello all, came across this forum yesterday whilst trying to sort out poor idle / stalling on the wife's 156 2.0 TS. Whilst most of the posts seem to refer to Selespeeds, I can confirm that the wire snip works as advertised on a manual box - sorted out the hunting immediately. Thanks to Marlon / Maverick, some good analysis / guesswork there! However the