Manny,
The car started to develop a slight loss of power at times. For example, when cruising at 80 mph steady, I could feel it hesitate just slightly (100 rpm drop). It also started to have a surging idle at times (intermittend up and down between 600 and 1000). Somwhere along the line the check engine light came on. And it now really hesitates on take off.
I had it read out and it indicated O2 sensor malfunction.
I bought both sensors and replaced them and reset the check engine light. The symptoms are the same after the new sensors and the light came right back on. I don't know if it is the same error code.
I checked the sensors and they are connected properly.
So my thoughts are cats or vacuum leak, but I am by no means an expert.
I apreciate everyones help,
Thanks,
Sab.

__________________
regards,
Sab.
'07 ML320 CDI (398 ft lbs / 1400 RPM)
'02CL 500
'91 928 GT Supercharged