Why does my 1998 Audi A3 1.8 Turbo idle high?

When my car is up to temperature it idles at around 1200rpm, it should be well under 1000rpm. Under full throttle it blows a little black smoke indicating that it may be running a bit rich?

An engine scan has brought up an error with the throttle body. My mechanic has recommended that the throttle body be replaced along with the coolant temperature sensor.

Does this seem like the right thing to do?

Thanks