[align=left]I have a 2000 S40 and it was running fine and all of a sudden the car had problems starting and it wouldn't idle without a foot on the gas.
To start the car we have to give it some gas. It won't start without it. Then we have to keep a foot on the gas during any stops. If we don't the car will sputter and die. It can't idle, but it is running smooth at higher rpms. We haven't gotten any check engine lights, but when it dies the battery light and the up arrow (suspension?) light turn on.
I have changed the fuel and air filters, but it is still doing it.

Any ideas?????????????
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Check all the hoses really good to make sure none are broke or have holes in them.
Espically the one that goes from the intake to the Intercooler.

 

the quick fix would be to set ur throttle wire to idle at 1500rpm that way u dont have to put ur foot on the gas all the time, but that wont solve the problem, it'll just keep it from bothering u

 

For a follow up, I did everything that was suggested from these forums (changed fuel filter, checked for vacuum leaks/broken hoses, checked fuses, etc.), and found out that it was a different problem.
Since the volvos tend to have problems with their ignition coils, this might happen to more people. The problem was the throttle body was fouled with carbon which in turn fouled the injectors and the spark plugs. After getting all of this clean out, it runs fine!