Why does my Bmw 320i goes 100% but when stoping at a stop light for about 15 seconds the car revs start to change and when i pull off it fells like the car is riding on 3 cylinders, i then stop turn the ignition off restart the car and then the car sounds 100% again. took it to bmw and they checked all the coils all ok took out catalytic converter still doing same thing what can it be black box or what

The is help in the link, and also in the BMW forums.

https://www.google.com/search?q=2016+BMW+320i+front+end+wiring+diagram

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Change the oil. The light will stop lit.

not enough info with or with out oil filter I start with 4 quarts and new oil filter start the engine run for 15 seconds shut off check the dip stick and add what the stick shows

It may be overdue for a scheduled tune-up, oil change, etc.

If you had work done on the car, they should have disconnected the battery. This "re-sets" the on-board computer to adjust to the new changes.

If you are referring to the "check engine" light as the "service light", here's what you can try:
disconnect the negative battery cable. Wait for 15 minutes, then re-connect. Hopefully that re-sets your on-board computer.

Some cars require a few more starts before the computer resets, so maybe you just haven't started it enough times since it was serviced.

Otherwise, I don't have enough info for a complete answer.

usually its goes by itself after putting the right amount of air in the tire, It take sometimes 15 minutes after the car runs. Good luck

Try locking with key in drivers door lock the urn to unlock position and hold 15 seconds should turn off alarm

Your oil is a little low, and the timing may be off a bit but if it smooths out after warm it is probably ljust
low oil.

check the linkage by the throttle
check for vaccum leaks

was your BMW over heated?