It's been reported here many times that the plat plugs cause bad idle problems in the 103 motors. Mine came with the H9DC0's and have never had anything else.
I would start with the spark plugs since the one's you've got are not right for your car.
I've never had an OVP issue but seem to recall reading here that an ABS light is oftens times indication of a problem with this part.
The OVP gets blamed for everything conceivable.
Look at M.B.DOCs comments in this thread.
how do you test an OVP to check if it's working?