Can you diagnose this idle problem?

A year 2000, 1.8 16v XU7JP4.

When the car has warmed up and is idling, there is an intermittent miss. I
call it a miss, but technically it probably isn't one. When in the car, you
can feel the car gentle vibrate then stop, vibrate then stop. Inside the
car, you can't hear an engine note change and the rev needle doesn't move.
You only feel it lightly 'shudder'.

If you are outside the car, you hear the engine and exhaust subtly labour,
then pick up again.

I have tried various plugs, have a new O2 sensor and air filter, have tried
various fuels, injection cleaners and have given the idle stepper motor and
throttle body a good clean. I've no fault codes, it drives perfectly, never
stalls and always starts.

I thought my recent O2 sensor had fixed it, but this morning, it came back.
The only difference between today and yesterday is the fact that today it is
very wet. I also wonder whether the idle stepper motor is being a little
sluggish, although it's not something I have heard of before.

 

It possibly when the A/C pump kicks in. Try knocking the a/c off and on
listen to the drop in revs.

 

Hello i think first you need to establish if it IS a misfire or a
characteristic of this engine type.The xu7 engine isn't the best peugeot
have made and don't really idle that well (in fact we haven't made a good
petrol yet!) and can be easily mistaken for a misfire as they are wank .
personally if i where you i'd save loads of time by just nipping it to your
local peugeot dealer and asking the master tech to have a quick look at it
to see if its "normal" or not.If normal they still may be able to flash the
e.c.u. then reinialise it .This makes a little difference but not
brilliant.also get him to read the e.c.u. for faults (even though they
don't always record any!!).If on the other hand he bursts out laughing and
say's its missing it's tits off ,you can then continue in your diagnostic
search or leave it at the dealer perhaps for him to "scope-it-out". let me
know how you get on ..
all the best... mark