My '03 MCS JCW running perfect went into the dealer for a check, as soon as it came out i noticed that every time you use the engine to slow you down when you get to 1200rpm the car seems to lose engine braking for a second and the thing jumps forward, (sometimes you can hear the transmission take a whack) and then all is ok and the engine braking continues to slow you. Took it back to the dealer and guess what- they say they did'nt do anything (just like they didn't scratch the roof). So my question is what kicks in at 1200rpm? and has anyone else got this fault?

 

Ok,

Engine braking is purely a function of the vacuum created in the cylinders by a closed throttle body ergo, the reason you would be seeing this would be because something is breaking the vacuum with the motor. That however is assuming that you actually are losing engine braking and it isnt something else that just feels similar.

 

This is perfectly normal. You're feeling the fuel injectors kicking back on, and 1200 RPM is right where it happens.

If your foot is off the gas pedal (and you don't have cruise control set) and the engine is turning 1200 RPM or faster, the fuel injectors are cut off completely because the engine doesn't need fuel. (Either you're engine braking or you're in neutral.)

But when the engine speed drops down close to idle, the ECU has to re-introduce fuel to keep the engine from stalling, so at 1200 RPM, it turns the fuel injectors back on. That's the little "kick" you're feeling. It's more noticeable in some gears than in others, but it's always there.

What was you car in the shop for? Could they have updated your software or done anything else that would have changed your throttle response?