156 wonky idle - THE FIX !!!!

A very big thankyou to Maverick for this info:

I can only assume that the wire Maverick talks about is what the ECU/ABS uses to stop the ABS activating at below 10mph or whatever it is. I tested my ABS by jumping on the brakes and it still works. Everything else is still working too. My idle is absolutely rock solid at about 800rpm with and without the aircon compressor on. The low speed driving, like in traffic jams, is so smooth now. No lurching or jumping as the car tries to rev.

I love Maverick (in a buddy slap on the back type of way of course )

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Normally while you are moving with the clutch in the idle in the alfa should stay at 1200rpm and drop to normal when stationery, the little trick removes the 1200rpm bit.

When the car was stationery the idle was rock solid.
When the car was moving with the clutch in it bounced between 500 and 1500 rpm, this was regardless of cars actual speed. By that i mean i could put clutch in at 70mph and let it return to idle and it would keep bouncing until the car stopped moving. I found it very dodgy approaching junctions.

DONT DISCONNECT THE PLUGS FROM SPEEDO BECAUSE YOU RISK THE AIRBAG LIGHT COMING ON AND IT WILL COST TO GET IT RESET.

On the back of the speedo there are 2 plugs A & B
ABS sends signal to pin 11 of connector A on the back of speedo.
This in turn is sent out on pin 15 of same connector to the ECU and also from pin 16 for the aircon.

I cut the wire coming from pin 15 and now my idle just settles to normal idle speed with no bouncing, except for 1 little dip with the aircon on and then it goes straight to normal idle and stays.

Glad it worked for you

I have the exact same problem!I just thought that the engine has a momentum of its own when pressing the clutch at high speeds(or not high at all,but when moving generally).
It does the same even if I put the gear stick in neutral...the needle bounces from 500 to 1500-2000 rpm until stopping

Yeah.
As soon as you mentioned the symptoms you were getting I knew I had the same problem. It seems that all my idle/compressor doodahs were down to the same thing.

Going by quite a few post on here about idle speed fluctuation, I reckon that most of us are suffereing from the same thing.

If it doesn't work for them they can always reconnect the wire, assuming they leave enough at the plug end to be able to strip it

I can't wait to coast along at 70mph with the clutch in now

Once again, thanks

Sounds like same problem, easy test is to disable ABS by removing the fuse and as that controls the speedo the ecu does not know the car is still moving.
Word of caution with ABS disabled EBD (electronic brake distribution) is also disabled so the rear wheels will lock up quite easy, but will be ok for a short test.

Hmmmm,does this trick work on a GTV TS?...

..I've had a similar problem with crazy revs at idle,when you are coming to a stop and the thing decides to idle at 1500-500-1500 rpm its not much fun.

...It comes and goes despite my entire induction/injection system having been thoroughly cleaned off the car as I presumed the idle valve or EGR valve were at fault.........usually fixed with an ECU reset which of course mucks the radio settings up.....

Time to get the snips out......

When exactly was EBD fitted to the 156, or did they all have it?

If they all have it, then Marlon's car is possibly quite strange. I say that because his car appeared to have chronic front brake fade at Knockhill.

I've noticed that on cars which come into the workshop which are fitted with EBD seem to stop very quickly. Because the rear bias is effectlively set correctly, I've noticed that the rear brakes on these cars seem to do a bit more work that on non EBD cars. That is of course the idea of EBD. It boosts rear effort initially to increase braking effect, and then lowers it to prevent rear brake locking.

That then asks the question why the front brakes on Marlon's car did so much of the work. I don't mean to worry you, Marlon, it could ok, and just my ignorance, but I just don't have much experience of working the brakes on a 156 very hard.

don't worry Ally, I too think the fronts of the 156 work too hard and it's evident with all the 156's I've seen at Knockhill. I've since put Red Dot XF pads on the front (temp stable to 950ºC) and that has stopped the fade after prolonged use. Saying that, at Knockhill, even the rear discs turned blue as you saw. So they were defo working hard. Maybe it's down to disc choice ??

Ok, fair point. I couldn't remember about the rear brakes. But does your car have EBD?

I dunno. It doesn't have a bias valve like the 155 so I imagine it probably will do.

I still have a similar problem on my Vauxhall Omega Estate. Very intermittent. The danger is that the engine can cut out on the approach to junctions or when slowing down generally so I lose the power steering which is a nightmare. My garage has tried everything with no permanent "cure". I will pass this info on, but just wanted everyone to know it's not just Alfas that have such problems.

Hi,

my 156 has these exact same symtoms. I'd love to try this solution but don't have a clue how to access the wires that Marlon describes. Can anyone please explain how to get to them without wrecking my dash?

Thanks

Andy

Cutting the wires sounds very drastic.

I had idling problems which were cured by sorting the idle actuator. I documented most of it on my website but basically having reset the idle actuator using AlfaDiag, the bouncing revs and stalling stopped. If ever I have to remove the throttle body now, I take the actuator off first to avoid it moving when disconnecting the throttle cable, etc. Then when it is put back it will be set at the correct starting position. Another reset and a throttle reset (90 secs) see it idle perfectly.

none of the reset stuff worked properly for my probs unfortunately. I thought it did, but the idle probs came back once the ECU relearned it's stuff

Andrew, there is a philips screw in the top of the speedo cowel. Undo the screw and the cowel will pull forward off. There is then 2 philips screws holding the speedo in place. remove these and pull the speedo forward. The wires are numbered on the plastic plugs. You will see on plug A, [1 8] on one side and [9 16] on the other. You have to look closeley as the numbers are small. You are looking for the wire at position 15.

Cheers Marlon. I'll have a look, hopefully this weekend as I have to replace the flasher unit too.

just a note.......if you cut the wire, make sure you leave enough at the plug end to be able to strip the wire back incase you need/want to reconnect it

I don't know the dates, but I know my s reg 156 doesn't have ebd.

You dont need to cut the wire to see if it works, just remove the fuse for the ABS so the speedo does not work, and go for a short drive.
If this sorts out your idle then move to the wire cutting stage.

Before i did this i had tried all the usual fixes
New MAF
New idle actuator
Cleaned throttlebody
Cleaned earth leads
Looked for air leaks
Had timing checked
Numerous resets on Examiner
Then bought AlfaDiag and reset it myself

All the mechanics just said thats what alfa`s do, not happy with that so decided to sort it myself and this was the result. Never had a problem with the idle since.

Originally Posted by Rob 156

I don't know the dates, but I know my s reg 156 doesn't have ebd.

Is it a UK spec car? Just asking as mine came with a bag full of brochures and leaflets. According to them it was standard fit across the 156 range from launch.

I'm gonna try cutting the wire too, I have exactly the same troubles Maverick describes.

This is all very worrying, the connection must be there for a purpose and from what I`ve read in this thread it sounds like you might be disabling the EBD?? Even if it isn`t that the ECU must want to know that information for a reason...?

EBD is only disabled with the ABS fuse removed(for testing), fully working when replaced.
I agree the connection must be there for some reason but nobody seems to know what, and mines been like this for about 6 months and never had any problems or side effects. The only reason i can see for it bieng there is so that the ECU knows the car is still moving therefore it tries to keep the idle at 1200rpm until its stationery, then it returns to normal.
Its seems that quite a lot of early cars have this problem so i tend to think its a problem with the early ECU`s or the signal on that wire has a problem. Everyones got a choice and mine was that i spent enough on this problem, this cured it and i`m happy. If people think its dodgy or the ECU is loosing vital info then they have a choice i am only sharing what i found out.

As I said earlier, I think the wire is there so that the ABS does not work below 10mph. Also as Maverick says, it keeps the idle at 1200rpm (should do anyway) when moving. This is too make moving off a bit smoother if not quite stationary as the revs have been raised to avoid the clutch grabbing or excessive slipping of the clutch.

My brakes work fine after doing the mod