amg_nik

Hello everyone, I recently purchased a 2007 SL55 from the original owner. It has only 60k miles, but I have some concerns. There is a weird issue when i am driving at a steady rate. Right around 2000 rpm, if i keep the throttle steady, the rpm needle jumps up and down about 50 or so rpm. I can feel the car not steady as well. I have a check engine light for p0422. In some places it says bad o2 sensor while others say the cats need replacing. I took the car apart last night on the top end and found a small oil leak from my valve cover gasket as well as a hole in my left intake tube (the black flex plastic tube connecting the airbox to the grill). Could the cel and intake tube be the cause of my problem? Not sure what it could be. My supercharger belt seems to be in good condition so i don't think it is a slipping issue. Thanks.

Oh and I am new to this forum! seems to be lots of enthusiasts

yoyo7112

first check the spark plugs and o2 sensor

Good luck !!

Nor Cal SL55

I don't think the valve cover leak or the plastic intake tube are your issue. I really don't have anything else constructive to add to your engine miss question, but WELCOME to the FORUM!!!

okbarnett

go with your diagnostics

amg_nik

I do not think the Valve cover gasket is my problem, just mentioned that i found the intake hole while replacing my gaskets. As far as diagnostics, I only have the one code for p0422 but there are some that say it is an o2 sensor while others say the cats need replacing. Maybe a spark plug issue? Any recommendations for spark plugs and wires? I hear evosport are good for wires but can't seem to find them. Thanks all!

carguyshu

buy OEM wires and the stock NGK spark plugs, but neither are likely your problem and the wires should be good for the life of the vehicle and the plugs good for 100k.

It is a code that the reading from your oxygen sensor is out of whack. This could mean the cat is bad or the oxygen sensor is bad. It is probably cheaper to start with the 02 sensor to see if that works. The cheapest place for MB parts I've found is huskerparts.com (they are an MB dealer that sells online).

If you are going to DIY at all on these cars you need to buy a STAR diagnostic setup. It is an investment that will pay for itself very quickly.