[shorod]

Welcome to the forum!

You might have better luck posting this in the vehicle-specific section. If you'd like this moved to the Volvo forum, let us know and someone will move it.

From a general discussion though, these symptoms would often suggest either a vacuum leak (which you say you've checked for) or a failing/failed Idle Air Control (IAC) servo. The IAC provides a path for air to bypass the throttle plate at idle and is controlled by the PCM. This allows the engine to idle faster when it's cold as well as compensate for engine loads from the A/C compressor, large electrical loads, hydraulic power steering at lock, etc. It basically does the same thing you are doing by pressing on the throttle to get the engine started and keep it running when cold.

Newer cars may not have an IAC, instead it may be incorporated in to the electronic throttle control (throttle by wire). However I don't think your '98 Volvo would have the throttle by wire system, so I expect it still uses an IAC.

-Rod