Help!

My 1999 C280 with 93,000 miles has trouble codes P0300 (random misfire) P0304, P0305, P0306 (misfires cylinders 4,5,6).

I've changed the 12 spark plugs.
I also changed both Oxygen sensors for bank 2 (drivers side) because I was also getting error codes for bad O2 sensors Bank 2, Sensors 1 & 2. Those error codes do not reappear now.
I pulled out the MAF to look at it (those tamper-proof torx screws are fun!). The MAF looks perfectly clean, but I did not know how to run any tests on it.

I've got a scan tool which I've used to reset the check engine light; it lights back up after about 1 minute of driving. And the car seems to have no power and runs rough.

Any ideas? Thank you very much for your help.
--Ron

 

Maybe your EGR valve is hung open.

 

I have the same car and same problem what is the EGR valave and where is it?

Thanks Al