Slow warm idle - dies (300E)

Hi,
I have a Brabus 3.6 based on a 300E (M103) which has just had it's head gasket changed, along with new valve guides. The car starts first time from
cold as it should holding a high 1200 RPM idle getting progressively slower as expected. The problem is that seemingly the warmer the engine gets the slower it tries to idle. By 85 degrees it wants to idle in drive (i.e. in traffic) at 500 RPM where it's just about alive but very uneasy, sometimes dying. Also at this slow RPM oil pressure can dip below 1 bar. I don't believe there is a prolem with the oil pressure because by 750 RPM it's at ~1.5 bar and at 3 bar by 1500RPM. Additionally the engine idles more erratically the hotter it gets, lumpily. It does have manual lifters so will never be silkily smooth I know. If I raise the revs to say, 750RPM the idle is noticibly smoother & do not believe it would cut out at this speed. Indeed when it warms I can drive it by left foot braking in traffic if necessary Engine power does not seem to done although the engine is still being "run-in" so I dare not stray over 4000RPM. I have searched forums for answers and the two most prominent are the overvoltage protection relay (OVP) & the idle control valve (ICV). I rempved the ICV today, it was clean but I sprayed some WD40 in it none-the-less. I turned the ignition on and saw it open then shut so it is functioning properly. The fuse on the OVP is also fine but I'm not sure how to check the OVP itself. I have also recently changed the air filter, the old one looked fine anyhow, no signs of the oil I'm used to seeing from the M110 motors. Any other possibilities? I fear it may be the bottom end, piston rings or cylinder bore causing a loss of compression but I would have thought this would be tagged with a loss of power and "smoking" both of which there aren't signs of.
Thanks for reading & helping if possible. Merry Christmas to all!!!
Mehmet
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ICV valve usually is very durable and long lasting. Since you said you got manual lifter... when is the last time you had it adjusted to spec? Manual lifter required valve adjustment every year.
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Just adjusted it when the head was put back on. I may re-adjust the lifters though just to make sure. Can they make such a difference?

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Oh yes!
Look for vacuum leaks also, any whistling sounds or improperly reconnected item?
Marty
PS Timing might also be an issue depending on who put things back together.
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