My recently acquired 89 DL auto starts violently - when the first cylinder fires, the engine stops (stalls the starter), then continues to crank, which will either start the engine or maybe fire violently again and stall the starter. The battery is hot, the starter seems powerful.

It seems like preignition, but it does it hot or cold.

Once running, it idles fast, just misses a little and has decent power - runs a little rough though. I changed ECU to a 951 and made no difference.

I threw the timing light on for fun (I know the ECU controls timing) and spark is way advanced at idle. I have an identical 89 DL and the timing is about TDC at slow idle. ANY ideas?