I have a 2010 B200 Turbo with 150,000 miles that when I am driving along at 60 mph all of a sudden it loses power and goes to like 20 mph maximum and if I shut the car off and restart it while it is rolling down the road it will restart and I can do 60 again for awhile and then for no reason it will drop again to 20 and no matter how far I press the gas peddle it will not go any faster. The first time this happened I got it going and it lasted with no problem most of the day I was in driving it, but next day it's it won't do that anymore it is just staying at 20 mph all the time. When it happens there are no check engine lights or codes or nothing to indicate what is the problem. I have AutoEnginuity software to check and I got no error. I took out the MAP and it says 5 volts. The signal wire voltage was fluctuating between .4 and .5. The car will sit there idling all day without dieing. I ordered another map but I did try taking it right out and it seemed to make no difference it still stayed in this limp mode.

 

UPDATE: We installed a brand new MAP sensor did not fix the problem. So after installing it I retried getting error codes and now get two error codes P0461 and P0238. The car will only do 20 mph maximum.

 

2nd Update: Also noticed today that the fuel gauge seems to work properly upon startup but about a minute or two it drops to empty.

 

3rd Update: I took it out for a test drive today for a 6 mile drive and the weird thing is the whole time it stayed at 20 mph except on the way back there is a medium sized hill it started slowing down and I wondered if I would even make it up the hill. As I was climbing all of a sudden it picked up speed to around 25 mph and it kept that increased speed for the extra mile home. As I said before it makes no difference how you press the gas pedal it goes the same slow speed. I don't want to throw parts at it but I need this fixed asap.