Hi

I've just changed my ABH engine on my Audi 100 S4 (the old one, with 214000 km was burning a lot of oil (3L / 500 km), the "new" one has 120000 km approx.)
From the old engine, I just kept the lambda sonde.

The engine is running well but I have a problem during acceleration : the engine is hesitating.

Instead of doing : vrrrrrrrrooooooooooouuuuuuuuuuuummmmmmmmmm
I have : vrrrrrr.....rrrrrrr......ooooooooo......uuuuuuuu.......mmmmmmmmmmmmmm (difficult to explain, it's not linear during acceleration)
I don't feel these hesitations beyond 3500 rpm.

With VAG-COM (not registered) there isn't any fault code. Maybe it'is a sensor, but vag-com don't let me to read them ! (I have a red error message instead of values : is it normal ???)

Maybe my ECU is deficient ?
Is there anyone who have an ECU to sold ?

Thanks