Yaris Sick When Cold.

[roya]

Hi everyone, I’m new to this so forgive me if it sounds wrong. I've got a yaris 1.5 sports 2001 which starts first time every time, but when I get 200 yards down the road and stop at a junction the engine revs drops and don't stop dropping until the engine stalls, this keeps on happening until the car has reached running temp. I’ve had three different mechanics look at the problem but they come to three different conclusions, the AA man says it could be air getting in to the system, the Toyota garage says it's a valve problem because the car is LPG converted, My usual mechanic says it's a problem with a sensor but can't identify which one.

Has anyone else had this problem, if so I need your help!!!!!!!!!!!!