low mpg on idle

[ronle]

hello, my manual 85 318 has low mpg all the time, except when coasting in gear.
is it a bad gauge, or if it is a real issue, how to troubleshoot it?
for reference, i'm getting about 230 miles on a full tank of 91, mostly city.

[82eye]

think the m10 gets around 20 - 24 mpg combined city / urban

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m10/161023-1984-318i-m10-fuel-mileage-help-from-the-people-driving-m10-s