I am new to forum and I want to thank everyone for their contributions they have helped me immensely. I own a 2002 ML 320 with 150,000 miles. When I started working on it there were 5 codes P0131, P0151, P0300, P0306, P0400. The right front O2 sensor had been replaced and the code hadn't changed. (Just before I got it.) I changed the spark plugs and the wires to eliminate any chance of that being a cause. They were original I put in Bosch just like stock. Wires were 90$ and plugs 7 each. Then I removed the egr valve pipe and it was about 40% plugged I cleaned it out and applied vacum to the egr valve with a piece of hose and my mouth and it moved freely seemed good to me. Then I removed the throttle body and cleaned it it was really bad on the back side of plate I seem to have a rough idle still it seems low to me about 750 rpm?? I will drive it more and see if I get codes to reapear. When I was test driving it there was power steering wine when turning the fluid level is good. So I have it right front wheel on a ramp sitting overnight. I am thinking I got air because the filter needs to be replaced. I looked everywhere for leaks and found none. I also looked for air intake leaks and found nothing.The seal around the intake housing and the throttle body seems iffy. I sprayed throttle body cleaner around it with the engine running and no difference in idle. Well that's where I am at at this point I am going to inspect the catilitic converters tomorrow. Any ideas on the low rough idle. Thanks! I updated my user info did I get it right? I now have P0400, P0131, P0137 codes. I removed and cleaned the EGR valve. I spent alot of time trying to find a vacuum or unmeasured air leak and didn't find one. If the O2 sensors are bad can that be the cause of the low/rough idle??