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!!!