Hello, I have 2002 S500.

I replaced the MAF.. and recovered a lot of power. I could not believe how much torque I got by replacing this sensor.

anyways, about 3 days later.........
Check Engine Light came on.

I do not have a code scanner. I might buy one for myself.

I don't think it is the gas- I checked the gas cap, but it was already tight. I did the gas cap again, but no luck even after 5 ignitions over 2 days.

Now, I am guessing if this could be related to O2 sensors. Any suggestions?

one more thing, when you remove the MAF sensor assembly, there is rubber notches on the rubber o-ring for sealing between 90 degree bent tube. This rubber is old, so it is pretty hard- I was not able to put the notches into the notch sockets on the 90 degree bent tube. could this let some unfiltered air to flow into the intake and trigger the engine check light?..

Please help!

 

No point inguessing why CEL came on. Get the codes read...anywhere should be able to do this very quickly.
Then we have something to b ase a diagnosis on.
If the tube between the MAF and the engine is incorrectly fitted it can alter the mixture which may well cause a misfire and the CEL to illuminate.
If the leak is on the filter size of the MAF it is unlikely that this will cause the CEL to illuminate but you are using unfiltered air will will cause undue engine wear over time.
Stuart

 

The job of the MAF is to determine exactly what volume of air is flowing into the engine at any time. Doing so allows the fuel injection system know exactly how much fuel is required to maintain the correct air fuel ratio. If the engine is getting unmetered air, then the volume of air is too large for the amount fuel and the mixture is too lean. Once it is too lean, it can set a code accordingly. The MAF and intake tract must be properly sealed.