i was thinking about buying a 318 BMW from 1991... i was wondering if anyone knows if it has a timing belt or chain and where can i find its specs online? is it a good car?

m40 series of engine driven by timing chain.
Engine is good, but rest of parts used in the car is... cheap.

You are better off getting E30 body 325 or 525.

Wiki BMW m42 to get the specification. Is it a good car? Yes, underpowered, but good.