2002 Peugeot 307 Stalling Problem

I have a peugeot 307 1.4 2002. It recently brokedown (engine went in to limp mode) and displayed a catalytic converter fault and would not hold its revs at idle (revs counter went to zero when gearbox put in to neutral and car stalled). I have replaced the spark plugs, coil pack and speed sensor as the computer was showing intermittent faults with ignition misfiring and vehicle speed sensor. Having replaced these parts the computer was cleared of the faults and redownloaded and is now showing no fault found. Also, the catalytic converter fault has not recurred. However, I still have a problem with the car in that it stalls when I stop quickly or slow down quickly - in which circumstances the revs counter drops to zero and the car stalls. I have to drive the car in such a way that the I keep the revs up and prevent the revs from dropping too quickly in order to stop the revs counter dropping to zero and the car stalling. I shall be grateful for your answer to this problem. In particular, could a fault have occured with the ECU (Sagem S2000-28) as a result of the misfire and speed sensor problems or is there a possible fault with another sensor that is not showing on the computer? Is has been suggested to me that the TDC sensor may be faulty.
Thank you for your assistance