When engine warms up it seems to idle a little rough

Hello, I have another question for you all. My van has A/C. When I first start the van up in the morning, the van idles real good, but once the engine warms up, it seems to idle a little rough. This is the way it does, fire-fire-fire-miss-fire-miss. You can really feel how the engine is running by putting the engine in Park, then go to the tailpipe and put your hand in front of the tailpipe and then you can really feel the engine miss. Driving down the highway or around town the engine doesn’t miss at all, except when you stop at a stop sign or stop light, then it starts missing again, but once you take off the engine smooths right out. Do you have any Idea's what might be causing this? The garage when I had my Van checked out for this problem, told me that the distributor, plugs, wires all check out okay, he then told me that the van needed motor mounts and transmission mounts replaced and that this would stop the engine from feeling like it was missing. I just can’t believe this. Need to know what you think. Will be waiting to hear from you. Thank you. Sincerely Bill H.