I have an used 2003 Audi A4 Quattro 3.0L V6 30V with roughly 93k miles on it. Two months ago I set out to replace the serpentine belt after it came off and I ended up having to replace the tensioner as well as the belt. Though that did not fix my problem because the belt kept slipping off. Come to find out that the power steering pump pulley was not seated properly. The screws in it had broken so after that was fixed, and I put the belt back on there was a somewhat thick cloud of white smoke coming from the back right of the engine, where the driver sits. In addition to the smoke the car sounded like it was losing power and preparing to cut off so I just turned the car off.
I'm thinking that happened because the engine hadn't been on longer than 20 seconds in 2 months. If that is the case what do I do, just allow the engine to run and smoke? or is there something I need to put in the engine or what?

I also replaced the spark plugs in addition to everything. Could that be why this is happening as well?

 

What kind of smell was the smoke?