I have an E320 2002 with 33,000miles on it.. The check engine light is on and the fuel cap is on correctly. When I accelerate the car splutters and does not run well at all. When I stop at a light it is as if the car does not change to a lower gear and I found out that shifting manually into 1st seems to help. Will just changing the MAS (I think that is what it is called) help all of these symptoms? Where is this sensor located?
Appreciate any help.
Alan

 

yes, this is the symptom of bad air mass sensor.

at the back of the engine, almost touching the firewall.