This is not the first E30 I have set up for Megasquirt, so I knew what I was doing. Being originally a Bosch Motronic 1.3 EMS, it's quite easy to convert. You only need a temperature sensor, and a replacement throttle sensor.
This time I did a full Plug and Play conversion, using an old ECU box & connector.
Under the MS board, are two PCB's that provide Wasted Spark output, 3-wire PWM Idle Control, Shift lights, Tacho, and two relay outputs.
The first thing you do with a converted E30, is toss the Air Flow Meter (AFM) in the bin. They sap your power, and too old to be of any use. Here I have put the IAT sensor in the air box, and attached a hose in the place of the AFM.
A coil pack replaces the dizzy. And I welded a bung in the exhaust for my JAW wideband sensor.
And the result? Much faster throttle response. Better fuel economy. Plus all the fun in tinkering with the settings.
And Next? I have an M30 3.5L engine to put in the car from a 735i. Also want to add a BeagleBoard & LCD display, probably with GPS, & GPRS.
Full writeup of the conversion, and how to make the Plug 'n Play ECU here: http://wiki.diyefi.co.uk