1997 E320 PO170 error code

I was wondering if you could give me your opinion about a car issue I am having. My 1997 E320 with 95k, is having a PO170 error code. It first came on a couple weeks ago and I had my mechanic look at it.
PO170 corresponds to "Fuel Trim 1" and there are a list of things this could be. For some reason Mechanic A doesn't think it's the Mass Air Flow sensor but Mechanic B does. I had a second opinion. I even brought it to AutoZone to have the code read... and sure enough it reads PO170 and he thought it could be an O2 sensor.
I've done a little research and from what I understand PO170 can be the MAF but usually it has two codes PO170 and PO173. My car is not driving abnormally. I can merge in and out of traffic and I can accelerate smoothly. Maybe my car is supposed to be more responsive and powerful? I don't know.
The second mechanic I went to practically specializes in Mercedes and his sister-in-law works with me. He mentioned that in his experience PO170 is the MAF. But, I was very concerned when it only took him 5 minutes to come to that conclusion.
Before I go to the Stdealer, I was wondering if you had any experience with this. I am frustrated with this situation because I am getting 3 different answers from 3 different good sources.
I posted this question for my nephew it is his car. Any help would be appreciated
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It is definitely the MAF sensor. We had the same problem on our 01 E320. It would only trigger one side fuel trim error... not both.
My suggestion is use the MAF cleaner and clean out the MAF unit... take it off the car and clean it well.... do not touch or break the wire inside the MAF. If it works, then you don't need to buy a new one.
If no change, buy a new MAF. You have to reset the code after you clean the MAF... same if you replace it.
O2 sensor is easy to diagnose... there are 4 on your car... front ones are fast changing readings... using OBD2 scanner... the rears on each side are slow changing... hold accelerator at a higher position and you will see the reading change slowly... If you got a zero on one... then bad 02 sensor... but on the scanner, you might misinterpretate it... because some scanners shows 8 units... just ignore the 4 zeros...
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You can try the MAF cleaner but make sure that you have a backup plan (e.g. number for a taxi to get you to/from the parts store with a new MAF). A lot of times the MAF itself does not go bad but the integrated temperature sensor starts reading extremely high, so cleaning the MAF does little good.
One cheap thing to check is the air filter and ensure that it is clean and that there are no obstructions in the air inlet.
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I owned the same model and had the same P0170 code with a Check Engine light after about 37K miles.
I had dealer check and estimate it - diagnosed MAF. I cleaned the MAF and it was OK for about a year. But then reoccurred at 40K miles so I installed a new MAF, bought from www.thebenzbin.com for about $230.
There are two types of MAF - the newer type has a rectangular electrical and the older style a round connector. Before ordering pull the connector off yours to see which is installed on your engine. Your's probably the newer type.
The MAF is simple to install one clamp and two snaps. Wet the rubber seal so it slides when you install the MAF. Keep everything clean as possible.
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Thanks for your helpfull replies I have passed them onto my Nephew.
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