I went and got an oil and filter change two days ago. I started the car today and my oil service light is now on when it never was on even beffore the change. WTF? 87 bmw 325i . What the hell did they do to my fn car!

Feels like walking into a conversation, but missing the first few paragraphs...

"This just started". Unfortunately, we don't know what "this" actually is, nor what light went out.

You did check the oil level, right?

That light just means the emission levels are too high,doesn't mean there is a big problem,a bad plug wire or even a loose fuel cap will turn on the light,

take the car to a part store they will run a scan for free

My car was doing the same thing, just today I took the day off and my neighbor, which is a mechanic told me that I probably need to clean the Idle control valve. I went to the local auto part store and bought a can of throttle body cleaner and a can of mass air flow sensor cleaner for a total of about $12.00 and he disassembled the throttle body and sprayed the parts for me while I revved the engine and that fixed it. My car now runs great.

http://www.obd-codes.com/p0440

sounds like someone has dislodged a cable somewhere in or around the oil filter area?'

Read all beffore starting. get all you need and get prepare beffore starting so you wont say any big word. Maybe have some safety glasses and never put youself on the way the oil would go out.
Buy yourself a 4.4L of new 10W30 motor oil, a oil filter, a little bucket of about 8" high and 24" round set of ratchett finaly some towel (for cleaning your tools and your hands if oiled by the old oil). Wait the motor to be cold. If you can, jack it a little bit just for you to be more comfortable under it. Better if you have ramp to put the front of the car on it and dont forget to put some safety like small candel and a tire stpper with the hand-brake on.
Go under the car, locate the oil pan and it's pug. Get the good size key or rattchet for the plug. Put you bucket under the plug, in line of the oil comming out, about 8 inches from the plug. Now unscrew the plug.... it will be a bit dirty and replace the buckey in line with the dirty oil if needed. When empty (about 10 minutes) get the oil cap on top of the motor out, go back under the car put the oil pan plug back (don't forget the washer and don't over tite it) , unscrew the old oil filter (watch for oil comming out from it also). With your finger, put some old oil on the rubber ring of the new oilf fliter and screw it in place of the old one "by hand", don't turn too hard, about half turn after the rubber touched the motor. Put the new oil in (where the oil cap on top-front of the motor was).. all the 4.4L. (watch for not putting oil all over, it will smell as hell when driving until it will all burn). Put the oil cap on. Recheck the filter, the oil pan plug and the oil cap. If all ok, Start the motor for 5 minutes but stay parked. Check the sound of the motor, it should go nicely ( by the way, get a full memory of this nice sound, it could alert you of somehting wrong if it dose not sound like this one day). Get you tools and the bucket from under the car, recheck the oil filter and the oil pan plug. If no oil is dripping, stop the car, get it down, get all things clear and clean. You can put the old oil in the can where was the new one beffore the job and get it back to your garage so they recycle it. The filter is gooing to the garbage. That's it. If not in a hurry and take your time with some good music and a coffee, you can do it in 20-45 minutes.
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Sounds like your valve seals are gone. Expensive, unless you can do it yourself.

I would talk to the tech where you had the oil changed to be certain even though it doesn't sound serious from your description.

I thought this was free support. Apparently I was wrong. How did I fix it? Easy, I broke down on the freeway and got towed home on a flatbed! That was easy!!