I have a 1998 S70 T5. It was my son's car for school. I haven't used it for about a month. I had to jump it to start it and let it idle for about 20 minutes to let the battery charge. After 20 minutes it started shaking and studdering. If I rev it up past 3000 it sounds ok but when it returns to idl...

I have a 1998 S70. When turn the key, a pump of somekind (air I think) begins to turn on. It remains on as long as the key in in the on position. I appears to be excessively noisy, being heard loudly over the engine idle. Is this normal? And whay kind of device is it?