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