Increasing mileage in 1990 BMW?

By my calculations that's about 15mpg which is way too low. You may need to repeat the injector cleaning a few times to get them completely clean. Doing it once can actually worsen things as you dislodge the build ups but not get rid of them. Another trick to try is to reset the ECU. This is very simple to do, just remove the negative wire from the battery and leave it for about an hour. This should be plenty long enough for the ECU to 'lose' its memory. Once you connect it back up drive as you normally would do and the ECU will learn your driving style.

you have done all that is reasonable, check that the tire pressures are ok, around 28. drive gently and allow the engine to cruise, there is no way that this engine will ever get the most in mileage because it was made before lean burn technology advances.

Changing the oil away from 20/50 to a 5 or 10/30 will also help

12) upload some nano gas saver into ur petrol tank 4 more effective pickup n gas saving. 13) swap off air con if needed. 14) take care of ur speed at eighty kpm n less than 15) do not carry heavy products in ur motor vehicle. sturdy success.

hi.i suggest to change the sparkplugs and the fuel pump in the tank and get a 16 size tire.and replace the fuel filter under the tank.

have a fuel tune done to it you clean out the throttle body and use a gas treatment to clean the fuel lines and injector and then they inject a chemical right into your intakes and intake valves giving you on average 3 to 8 miles to a gallon of gas