Hello, I'm looking at purchasing a 1994 e420 and it appears to have a bad air flow sensor(hardly revs over 1500 RPM, no differance in the way it runs when AFS is unplugged. is there any way to check the sensor to see if it is bad other than running a cel light to tell you it is bad. BTW how do you run the CEL light and what are the codes, Thank you in advance