2006 Other Fiat Models High Idle after Stop Go Traffic

Hi, I really hope yo guys could help me out with this.

I have a FIAT with a 1.6 liter engine. (Petrol 4 cylinder, 100BHP, 16 Valve, 1596CC, DOHC).

I have been experiencing a very wierd problem. When ever i have to move through bumper to bumper (stop and go) traffic, the idle rpm sticks to 1100 mark. If the car is switched off and turned on immediately everything is back to normal untill the next bumper to bumper traffic situation. It happens mostly during hot conditions (more frequently during afternoon). During colder conditions the car takes much longer tine before it starts showing this behaviour.

Have changed the following parts till now but could not solve the issue
- ECU
- Throttle Body
- IAC valve
- Throttle position sensor
- rpm sensor
- Air pressure sensor.

The car runs perfectly fine on highways when movement is at igher speeds. I have done around 300km trip and the idle was perfect at 650 rpm when parked in idle. But as soon as it enters a traffic situation, the idle moves up to 1100 and sticks there.

Hope to hear from you soon.