Heat output problem with W123 300D

[240diowa]

Can someone help me diagnose my heat output problem? I only get heat when I'm cruising down the road and even then it isn't much, I basically get no heat at Idle. Don't know if it is the mono-valve or the auxilary water pump. Some threads I read say that if you get heat at idle and none at operating then it's the monovalve, I kinda have the opposite. My kids are freezing in the morning...