my 94 bmw 325i has a idle problem it drops down and back up to normal (car shakes) car has not stalled. also the car has no power or get up and go.

just changed spark plugs, all hoses were checked for tears or cracks. throttle body cleaned.

the only part that i know has to be replaced is one of my injectors. looked pretty bad when i took them out but the rest are fine.

check engine light is on. brought the car to shop to scan codes but the place i had brought it supposedly does not have a scanner where it reads the codes, which ever scanner they had, they told me it was my O2 sensor.

where should i start? dont want to waist the time and money on parts that i dont need.