1991 240 Code 242 long term fuel trim at idle

[epops]

Have an otherwise well running 240 wagon with a code 242. Last year the car failed emissions due to high CO readings. Paid a garage $900 to get a waiver after replacing cap rotor and plugs, O2 sensor, converter, throtle position sensor, fuel pressure regulator, radiator bottle and air filter. Cleaned injectors, air mass meter and checked timing. After erasure, the code reapears after 100 miles or so of city driving. The car gets about 16 mpg, which is about 2 or 3 mpg less than what it used to get in stop and go traffic a few years back.