Thanks again for all the help guys. I don't have a lot of experience with Mercedes so the experience of the people on here is a massive help.
Whilst checking the fuses I found that someone had used the wrong fuse in the fuse board beside the battery (under the rear seat). Position 7 should have been a 7.5 but someone had use a 4 and it had blown! Changed it and I've got my tachometer back! Nothing I've researched online or on the fuse holder guides says that this fuse should be related to the tachometer!
So I've still got a rough idle (starts and idles fine at first but then surges a bit). Anyone know where the ICS (Idle control sensor) lives on these cars??
Also the heater is still blowing hot air when on full cold! Anyone got any idea's where to look for problems here? I'm reluctant to think it would just be low refrigerant in the A/C as surely that wouldn't cause the air to be hot but hey ho this car has a mind of it's own so guess I can't rule that out!