Matrix 2002 Weird Behaviour

[thetristan]

Hi all
It started 6 months ago and it gets worse every day.I have a 1600 cc Matrix (fuel benzin)
When i (try) to start the motor in the morning when its still cold it takes 5 to 6 times to turn the key to start.
And when it does it works on 1100 rpm (i think thats right when its cold).
If i press the throttle the rpms fall from 1100 to 200 - 300 and most of the times motor goes off. Sometimes though (2-3 seconds after i removed my foot from throttle) rpms fly from 300 to 3500 and then fall to 1100 again.
If i put 1st gear and start moving the car it drives on 300 rpm !!! and it jumps like a donkey.
When the motor gets warm all theese are history. It works ok on 800 rpm without foot on throttle (stopped). and drives ok on every gear.
Check Engine light is on and on the garage they told me that the problem list from the check was very long.
They think that all this is caused by the sensor that is on the catalysator (lamda sensor called here in Greece).
I will try to have the problem codes to share it with you.
Until then could you advise something?