1984 W123 230CE (or 230E I guess) Cold idle speed question

Not sure I have a problem, but when the car is cold (1st start in the AM), it idles too slowly and is very 'juddery'. Putting it in D helps a little (as the vacuum controlled ignition retard function is turned
aff), but its still too slow when drive is taken up (at idle). It drives fine, so I feel the warm up regulator is richening it up OK.
I have changed the electrically heated Aux air valve for another (not a new one however), but the effect is the same.
When the engine warms through, the idle speed is ~800 and nice and smooth. Also the CO content is spot on at this point too.
Can anyone tell me what their late 123 series 230E (or CE) does (rpm wise etc) when cold at idle?
Any suggestions about what to check?
Cheers... Rob.
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