406 V6 3.0 lumpy tick over

Hello All,
My 406 3.0 V6 seems to idle in a lumpy fashion.
With all the electrical extras off i.e. lights, fans, heaters, AC and the
steering wheel not moving and foot off the brake:
The cars idle speed fluctuates, well more dips occasionally. Not
periodically but every 20 seconds or so. Most of the time the car recovers,
it seems by applying is own amount of throttle. Other times it stalls
(particularly when facing down a hill or approaching round-abouts).
When you put your foot lightly on the accelerator to take the engine what
would be 1000RPM the engine actually fluctuates between 600RPM and 1100RPM.
Kind of like it is an unstable system with to much overshoot. Other than
that it works flawlessly.

I have had the coil, spark plugs and leads changed to no effect. I have had
the ECU log monitored over the period of a week or so but nothing is coming
up at all. I am guessing that this is a sensor that is not reading
correctly.

Does anyone have a copy of a system diagram or can tell me what sensors
effect the idling speed ? Or know of if this is a common fault? Does anyone
else's V6 not have a rock solid idle speed?

Regards

Gary

 

I have made a movie on my phone of it. It should play in quicktime.
http://www.garycadman.com/MOV00008.MP4
It starts off fluctuating a little then half way through I increase the revs
and it starts fluctating quite a lot. This is not me reving it up and down.

 

This sounds a lot like the old idle-speed stepper motor problem.
I've had that problem with those exact symptoms on other motors,
but have no idea if the V6 406 suffers with it or even has one.

djimbo.

 

I've had the same vehicle - 3l V6 - for years and I have noticed, when
idling, that it occasionally gives itself a touch of the accelerator.
Or that is what is feels/sounds like.

I assume it is an artifact of the engine management system and serves
some purpose. It has never bothered me - nice to think that the engine
can look after itself.

 

I had one too for 8 years (new in Feb '98) - automatic - and it did the
same. Early on it started cutting out intermittently when slowing to a stop,
like at lights or a junction. Can't remember now the exact details, but I
*think* it was fixed by fitting a new engine management chip or something. I
also have some recollection of it being covered by a Peugeot recall, but I
may be wrong. Anyway, after the fix it was fine, but always did this
slightly irregular idle.

 

Do you know where this is located? Unfortunately they don't do a Haynes
manual for the V6 engine.

Regards
G

 

I had a similar problem on my 406 HDI, turned out to be the lambda
sensor. I think this lies in the exhaust path and detects the amount of
oxygen in the exhaust and adjusts the fuel mix accordingly. Once this
was changed I had no futher problems.

Neil.

 

How much did this sensor cost? If you don't mind me asking?

Regards
Gary

 

I have a 3.0 V6 Auto. Like Ken's, it does occasionally "give itself a
touch on the accelerator", but your problem is MUCH more significant
than what happens with mine. If you spend a lot of time in traffic, I
should think your fuel economy is suffering from this too.