[W126 Coupe] HELP! Car Salling!!!!!

[David Fatovic]

I need some help with my dad's 85 500SEL.  The car
seems to stall when it gets warm.  The strange thing
is, it doesn't seem to be only when the car is at
idle.  But driving down the highway the car will stall
out.  My dad took it to one mechanic who changed some
vacuum tubes and then charged him to change the
ignition control unit (which I have replaced before). 
Now if it was the ignition control unit the car would
not start at all because it wouldn't be telling the
coil to release its charge.  But after the car stalls
it starts up again. 

So I am thinking that the mechanic just took us for a
ride, but I don't know what else it could be.  I know
people have had this issue or something similar
before.  

Any ideas on what we should look at?

Thanks,

David