3.0 V6 406 rough idle

I have a 3.0 V6 and have been trying to chase down why it would not idle
smoothly, it intermittently (every ~10 seconds) fluctuates by about +/-
300rpm.
I have changed:
Idle control Valve,
Throttle potentiometer,
Coil pack,
HT leads,
Spark plugs,
Lambda sensor,
MAF sensor,
Inlet manifold gaskets.

I also have my own Code reader that I can view the log files with and
nothing is coming up at all over 3 months (must be a record in its self).
Does anyone know what might cause a this intermittent bad idling and
stalling when steering, parking and edging in traffic?
Sometimes misfires for the first 5 seconds in the morning as well and does
appear to be worst when the car is facing down hill. Performs just fine
through the rev range. Temperature makes no difference but it does like damp
mornings.

Regards
Gary

 

Dos this car tick over when warm? try reseating the coil pack make sure
it is very clean under it.if you hold revs at 2000 rpm dos it hold or
dos it miss fire? tappet setting?
good luck from chris Addlestone Surrey

 

Have you tried a dose of injector cleaner jollop? Our 306XT can be
difficult to start (needs full throttle) when facing uphill which I put down
to leaking injectors flooding the thing. If yours is similarly gradient
sensitive it's more likely to be something like this than the coil pack.
Cars always run better when the air is damp because it is denser then.

Ron Robinson

 

I just noticed the response by chris to this posting, my 406 2ltr petrol has
a
'miss' at 2000 revs, the post implies that you may know what causes this,
am I right? My local garage(s) have not been able to cure it, its very
irritating to say the least, any help appreciated.Sorry if its regarded as
'off topic'
thanks
John

 

Thanks for your input.

The car does tick over when warm but the problem is still there. It will
also stall once warm.
If you hold it at say 2500rpm the rev range wanders by the same amount.
It is as if a sensor is trying to incorrectly compensate for something.

G.

 

John,

The only thing I can think of is that this might be the change over beween
idle and mid on the throttle potentiometer. You could check it out by
disconnecting it, the ECU will do it's best to compensate but it will not be
able to tell either way, hence bypassing it.

Regards
Gary

 

thanks for that Gary, I will give it a try,
best wishes
John