Cold start low idle
 

I have a '93 190E. Recently the battery was connected to the wrong terminals in the dark by a helpful brother in law! As a result the ABS light remained constantly on and the car struggles to start when cold.

A local MB specialist suggested it was a relay that had blown and replaced it, this resulted in the ABS light no longer being constantly on, but did not rectify the starting problem.

The MB specialist has subsequently replaced the idle valve at great expense and is now stumped as to what the problem is. They are suggesting that is maybe the O2 sensor.

Any help/ideas would be greatly appreciated.