Strange Acceleration / Performance behaviour - E46 '99 318 Saloon

Maybe the temperature sensor for the computer DME is bad or has dodgy wiring. The engine could be in cold start mode all the time.

Auuto?

Sounds like an effect of whether the gearbox oil is cold or hot.

I'd say you are shifting way too soon. BMW engines are made to rev much higher even under normal conditions...

..but why should it work when cold and not when hot?

It's small problems like this and very poor customer service that can make owning a newish BMW a very bad experience. Usually it's a case of "computer says no" when you think there might be a problem.

many thanks for the info..

it is a manual...

It is true that the clutch is smoother when the engine is cold. After a couple of miles the clutch hasn't the same smooth feeling.

But how could the gearbox oil be related with the above behavior ?

BR / M

I see your point... it is also the case the performance feels poor when the engine is at normal temp and I shift gears at higher revs - the MPG indicator also shows higher consumption.

What else could it be assuming same behavior on gear shifting at higher revs ?

BR / M

Sounds to me like you are running rich. I'd get someone to run diagnostics on it.

Well, the engine management system changes the amount of fuel needed when the engine warms up. My guess is that this changes the characteristics of the engine a bit. I would make sure all sensors are clean (in the intake) and make sure there are no stored codes.

Read the codes.

Well, it could be that your O2 sensor is going bad. In the first few minutes of cold operation the ECU is running "open loop" (meaning without the O2 sensor feedback) until the sensor is deemed to be fully up to operating temperature. Once it does go "closed loop" if the feedback signal from the sensor is wrong for any reason the engine will run rich or lean. Eventually the signal will exceed hard limits coded into the ECU and it will throw a "check engine" code.

A quick exhaust gas analysis at a competent shop should tell if that is what is going on...

Ding ding ding, we have a winner.... maybe... But the engine should really be running like crap if the O2 sensor is bad... But this car probably has 2 or 4 O2 sensors like my 96 M3, and so I would think some codes would be getting set. I guess 318, probably 2 sensors.

Thanks, Mark