I have a little tool design you can make for about $5 [US]
email if you want a jpg of the parts/schematic.. it is in pictoral form for
those not familiar w/schematic symbols....
This will get you the stored codes and you can list them.
Also, the common faults in line with your complaints are the 3 plug to coil
connectors under each coil.. They are cheap and we have learned to change them
whever changing plugs [Have found Beru best bet]
The other check you should make is the Over Voltage relay .. it is behind the
panel near battery..aluminum rectangular can w/fuse on top
If it has the original part# 000 540-52-45, change it to 000 540 67