is it normal to have after a head gasket replacemente a rough idle and problems when acelerating?

 

Of course not! I am thinking possibly a vacuum leak. I would test for a vacuum leak with a gauge. This test takes a few minutes and is easy to find a vacuum port. Are you certain the timing belt was installed properly as well? Any check engine light steadily illuminated or flashing?

 

no CEL, the engine dies as at red lights and stop signs... The mechanic I went says the car needs time and miles to settle down. He says also the timing belt is installed properly and double checked it.

 

He is a poor mechanic! I would expect he would return the car running and relearned if re-learning is needed. Who repairs a car to the customer when it stalls out in traffic and replies Ummm just keep driving it until it works the bugs out of the computer!
1. Does the car start easily after stalling at lights and stop signs?
2. Does the idle get smoother as the car warms up from a cold start?
3. How mechanically inclined are you?
4. Is the mechanic a licensed business?

a few things come to mind. Vacuum operated EGR valves stick open and stall the engine at complete stops but I am not sure if the 1.7 has a vacuum or electric EGR. A vacuum gauge will reveal a lot of things about the engine performance.