The Economy gauge doesn't measure fuel useage, just vacuum depression in the intake manifold. You can be in Economy Gauge Green with some serious cruising velocity at the wheels
Your idle speed doesn't sound much different to the hot idle speed on my Euro 300TE (same engine), but cold idle should be about 1000rpm at first. The only time we didn't get this was when there was a difficult cold starting problem that turned out to be the OVP relay had failed and was not switching on the cold start fuel injector.
General rough idling is often worn engine mounts on those M103 engines.