stalling 'slowing' problem.
 

Hi guys,i currently have a problem with my X6 before i start i would like to say ive had three Xedos6's before and none of them have ever done this so i know it might not be a common fault.

My problem is when im going about 40-50mph and let go of the throttle so the car is slowing down with the gear im getting a slight (sometimes quite violent) judder,with the rev counter jumping up,feels like a little stall with the engine.(not slowing down smoothly).

At first i thought it was the brake so i knocked it into N at the same speed and it slowed down perfectly as it should,and smoothly.

i have only bought this car very recently so im not to used to the cars habbits yet,i don't know if it has done this for ages or not but all i know is that it is not normal as this is my 4th and none of the others have done this before,i think it maybe air flow but in not sure what to do or what action to take.

once again thank you all very much,you have been most helpful with my problems :)

gogboy.

Hi,

First off all is it a manual or automatic gearbox?
When you let go the throttle above a certain speed, the injection times of fuel are determined by a fixed table. Under a certain speed the O2 lamda sensors in combination with the airflow sensor. take over again.
It could be that the lambda sensors or airflow sensor are too far gone and that there is a jump in injection times when the engine switches from the table to the lambda control.
This could result in a ramp up of the revs.
You can check the lambda sensors with a oscilloscope.

Regards Maurice

Ahh thank you very much that makes sense,its an Automatic.
i have another X6 so i will swap over the mass air flow sensor and see if that makes a difference if not you say the lambda sensor next. i know about the MAS sensor but i dont know where the lambda sensor is,could you tell me where it is and is it easy to replace? thanks for the help :)

The lambda sensors are in the exhaust manifold. There are 2 lambda sensors, 1 for each cilinderbank. One is quite easy to find, between the radiator and the engine. The second (rear bank) is a bit more tricky.
Before replacing them I would try to measure them to see if you get a oscilating signal between 0 and 1 volt.