If you want a proper electronics project, try linking the ECU into a GPS. For bonus points, tie it into a forward facing camera.
At present the ECU only considers what the driver is telling it - how hard the accelerator is being pressed, what the intake temperature is. If the ECU knew more about the road being travelled, then it could make better decisions about the amount of fuel to inject. So, it could go as lean as possible cruising on a busy motorway, and with a camera it could lean out as you were approaching a queue of traffic. If you gave it a fair amount of memory, it could remember how you drove, and optimise for the style you use on a particular road, eg,:
- He's going home on the M3, he always sticks at 70, optimise for economy above all else
- He's now off the M3, and driving home, this is where he rags it, when he asks for power, give him all you've got and stuff the consumption.
Back to OP. When the yellow engine light goes on, diagnostics gives me a clue where to start looking. With my 156, it is usually the accelerator pedal connector....