i have a bmw 325i 1991 2-door automatic. my check engine light comes on and stays on until i reset it by disconnecting the battery.
i have noticed that the light only comes on under the following conditions.
1. any time my rpm goes over 3000 rpm - this can be during acceleration or if i am cruising on the highway.
2. whenever i suddenly depress the accelerator... such as when i want to make a powerful take-off from stand-still.
moments before the check engine light comes on, the motor completely misfires, almost stalls and then comes back to life. after the check engine warning light is on the problem disappears....i think monotronic goes into some default mode because the car chews gasoline bad until i reset the light.
after reseting the light, if i make a gradual take-off or dont exceed 3000 rpm the motor does not misfire and the light never comes on.
the motor idles very well. i have changed all the hoses and clips to eliminate air leaks. i changed my spark plugs to bmw dealer recommended. i changed the mass air-flow meter. i changed the oxygen sensor. i re-adjusted the throttle position sensor. i tested the idle air stabilizer and the specs are within those recommended in the bentley manual. i changed the fuel filter, air filter and even the oil and oil filter.