1. Have a smoke test done to locate air leaks.
2, The idle control valve should be buzzing quietly with the key to 'ON' engine off.
3, There are a pair of sensors in the bellhousing by the driver's feet. One tells the computer where the engine is in the firing cycle and the second tells the computer what the engine speed is. The connectors for these sensors are on the fire wall. A crude test for these sensors is to measure the resistance...values are on any E30 site.
4, Make sure that the engine coolant sensor is within resistance spec.
5, Make sure the ignition system is in tune.
6, make sure that the injectors are not leaking.