My BMW 520i 1998, is not powering beyond 20 mph.?

My 520i 1998, is not powering beyond 20 mph. The car starts OK and moves normally in 1st gear at about 5-10 mph but when i try to accelerate it fails to power up even when i change to higher gears. It almost starts rolling on its own and then suddenly kind of jerks and accelerate for to about 20 mph then slows down again. Its been electronically diagnosed twice first by the AA and then a local garage and its coming up with no faults on the system. Local garage tried changing the mass flow meter and lambda probe but there is no change.

Does any one know whats causing this and how to fix it? Please help.

My BMW 520i 1998, is not powering beyond 20 mph.?agv

Goalaso0 is right. Have it diagnosed by a BMW dealer.

Pay the minimum diagnostic fee of one hour. Then take it from there (meaning, since you presumably already know what is wrong after diagnosis, then you can have it repaired by somebody else who charges less, or you can do it yourself).

I do not believe that there is no fault whatsoever. Most probably, the people who looked into your car do not have the proper diagnostic tools.

There are so many things that could cause your problem.

Notably the fuel supply system or the cam sensors. But sight unseen, and with faults unknown, I do not want to guess or be a prophet.

My BMW 520i 1998, is not powering beyond 20 mph.?antivirus software

Your car is in limp mode. cylinders have been cut off to save the engine from any damage. Take it to your nearest BMW dealer.