I have a 1999 ml430, its acceleration use to be a beauty, but now its response is very poor even when i completely throttle down. Secondly I cannot exceed 100MPH even with the gas pedal completely throttled down. I have replaced the MAF but to no avail. My Mech is suggesting I change the fuel pump, can anyone assist me please

 

I just posted twice in the E-CLASS procedure of testing fuel pump delivery volume. You may have just clogged fuel filter and the pump can't push enough fuel through it.

 

Hi Thanks, have just had my engine scanned with an OBD tool and it is showing me code PO 715; input/turbine speed sensor ckt malfunction. How do I go from here?

 

Sorry for the delay, it seems like no one here ever had your symptoms or guys are bussy and have no time for reading/reply.
P0715 code is for speed/RPM sensor.
It could also be supply voltage for speed sensor.
Fist I would unplug electric connector to your transmission and see if it is not full of fluid, clean it with contact cleaner spray and dry it with burst of clean air.
If this doesn't help, you have to check the RPM sensors inside the transmission. Could be bad sensor, dirty with metal particles stock to the tip of it or loose reference wheel.
Dealer should be able to scan the transmission module for closer diagnosing then my 163 ML Star Manual.
Good luck and Happy Holidays,
Bernard