Revolutionized cold start + exhaust pipe

Hello!

I have an Astra 1.8 16V Dek year 1999, and usually sleep in the street.

The fact is that when I start the car, it is revolutionized at first until 2,000 is for about 3 seconds and then it starts to go down to 1,500, then what I do is give a touch to the accelerator and that is when it goes down to a normal state, 1000 revolutions.

Why does this always do this? is the car cold? Any problem with oil?

I have the escape tube with a hole, since I listen to a noise, I do not know if it can be related, I understand that no, but I am not an expert ..

Anyway, I hope it is little the joke ... Anyone knows if to change the escape tube of the Opel Astra you have to change it whole or is it sectioned?

THANK YOU!!!!

Cold renewals would have to climb at 1200RPM approx and measure that it heats down around 800.Tu failure may be due to an air intake in the admission or that the idle valve is dirty. It is cleaned with mural 5000.The exhaust tube is separated into three sections.