[dkmr]

My 87 325is had a similar problem but would not get better when it warmed up. After about a week in the shop they finally diagnosed it to be a leaky intake manifold gasket, which was installed impropperly by the previous owner. The shop fixed it and all was good. Then about a year after it started to do it again. The first thing I did was pull the intake and look at the gasket. Sure enough they didn't put the gasket on right and it blew out the little bit that was sealing it. New gaskets and some sealant solved the problem. A year and a half later and it's still running fine.

Hope this helps you out!