Just an update to all out there.
I posted a thread a while back, W124, E200, surging idle when cold, occasional failure to start when warm.
Had a few good replies, and also spent a while in the database.
Most pointed as first port-of-call to the OVP.
I thought I'd save a few quid and get a second hand one (yes I know a new one is £40, $60 odd, but I thought it worth a try,)
"New" one (2nd hand) cost me £20- $30 -and I still had similar problems PLUS, a misfire for 30 seconds or so, about 2 minutes into a cold start.
Well, I bit the bullet yesterday. Bought a brand new one.
My car is overjoyed.
So am I. The car runs like new. Better than I can ever remember.

So the moral of this ramble is: The OVP is so vital, don't be a tight-arse like me. Buy a new one.
Thanks all for your help.

Barry

E200 wagon 1994 108,000 miles. Now runs like new.