Much like my e30 m30, the needles on the gauges jumped all around. When running, you could tap on the speedo and the rpms would jump up. The gas guage seemed to only show either full or empty. This is a typical problem with BMW guage clusters from this era. It is usually either a set of batteries leaking and corroding circuit boards, and/or cold solder joints. Kind of an annoyance, but the real bothersome piece was not knowing if the temperature guage could be trusted.
So I yanked the cluster out and completely disassembled it. The batteries were in decent shape, but they were replaced and relocated external to the cluster. Found a whole row of bad solder joints - check out the pictures below.