A surging idle is not caused by a plugged cat.

I'd check for:

1. vacum leak
2. bad mass air meter
3. bad throttle actuator

You also need to replace your engine wiring harness before you do any other diagnostic work.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".