99 volvo starts but stalls

My car sometimes stalls two or three seconds after starting. The starter always works perfectly, but as the RPMs fall below 1000 or so, it dies. If I wait a few minutes, it will usually start up with no problem, though not always the first time. Sometimes I have to give it a little gas to keep the RPMs up for long enough to get it to idle properly (I know that’s not great for the engine). I have noticed that this happens when I try to start the car soon after a very short drive (running errands in the neighborhood, for example) and more often when it’s been raining or it’s humid. My mechanics did a tuneup, which helped for a while, but it’s happening again. Any thoughts?

If it is humidity related the most probable cause is plug wires, or a distributor cap. You may be able to use a spray bottle of water and isolate the source of the problem. Other symptoms non water related can be checked by the mechanic when it is in failure mode. It could be a weak fuel pump or injector problems.