Mine have always been happy at around 750 in Park or Neutral.

On the surging. Since you have an aftermarket computer and frequency valve, you will probably not be able to test the on-off ratio like you would on a US car.

I would suggest connecting the positive side of your meter to the o2 sensor and ground the negative. With the car at idle and completely warmed up (as in drive it) adjust the mixture until you get .75-.85 volts. Reconnect the sensor. If the rest of the setup is good, that should stop the surging. If it doesn't stop it, then just leave it.

This basically uses the sensor voltage to tune the mixture. Worked very well on one of my 280SL's.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe