Boxter problem.I need your help please.
 

I have a 99 boxster tiptronic with 21000km.I haven't drove it for 3 month.I finally took it out a few weeks ago and at a red light the check engine light came on and the car just stalled.On another occasion another red light the rpm went down and up again as if the engine were strugleling.On the highway sometime,the check engine light would light up for a second,feel a small jerk and light goes off without stalling.Only stalls on a complete stop(on drive and park).I brought it to the porsche dealership.They kept it for about a week because it had not stalled on them.When it finally did,they checked the codes and said 2 relay had to be change.Made the repairs,2 days later the same problems comes back.So before I bring it back to the dealer.I would like you advice on what may be wrong.I think it might be the o2 sensors or the fuel pump.I do not wanna pay for other costly repairs I don't need.
Thanks for any advice guys.

Sounds to me like the o2 sensor or sensors. From the sound of the throttle hunting some at idle that is usually cause by a bad sensor or potentially bad gas. I might suggest putting a fuel additive in your next fillup and see how it acts. No improvement I might suggest start by replacing your sensors. I might start with the Mass Air flow sensor and maybe look into the sensors on your exhaust.

What relays/parts were replaced. Part numbers if you have them.

Tool Pants: I not sure but I remember I will try to find out.

I don't understand how o2 sensors can cut an engine off(I am not familar with mechanis)And why this happens only when I am to a complete stop??

Well that is when it would happen. At low RPM's the o2 sensors try to adjust and are unable to. As a result the RPM starts "hunting" looking to adjust its air/fuel mixture and is unable to and will sometimes cutoff. I replaced all of my o2 sensors this last summer due to a simular hunting problem.

There is 2 o2 sensors right?? Do you remember how much it cost??
Thanks for your advice.I appreciate it !!