I'm not an expert, but I do have the same car as you and I can at least give some general check points that you might want to consider.
As far as I know, the RPM needle bouncing would be a cylinder (or a few) misfiring..the amount of bouncing would be dependent on how many are cylinders are not operating correctly. This would indicate either a timing issue, or an actual ignition issue, because I don't believe the engine is actually making contact with your transmission while in park
If it's an ignition issue it could be dirty/faulty fuel injectors not injecting enough gas, spark plugs not igniting the fuel completely, or even bad spark plug wires; or possibly a combination of them all. These are all things you can swap out yourself simply by taking a trip to autozone and buying the parts. It's as simple as popping the plug wires off, unscrewing the spark plugs and inserting new ones and then replacing the plug wires accordingly. I recently had to do this myself for the first time ever, and it was the easiest thing I've ever done to my car and it now idles so perfectly I can't tell if it's running or not. Your best bet is to take it to a quick tune up shop, or if you're a DYI'er, go to autozone and grab some fuel injector cleaner (4-5 bucks), NGK premium spark plugs (10 for 4), spark plug wires (20-40 for a set) and the spark plug puller is 20 dollars. Regardless, if it does turn out to be the ignition, it's usually not very pricey unless it's the fuel injectors and those can go for 80-150 a piece...so definitely invest in a bottle of cleaner before getting them swapped and just talking to an autozone employee for 10-15 will net you a good chunk of knowledge--they'll verbally walk you through the steps if they think they know what the issue is.
Beyond the simple ignition, I can't give too much advice. But you may want to have the transmission and timing belt checked if you're driving in mountainous regions. My friend's 1997 ford taurus is running into similar issues, but while actually in drive; his transmission is slowly "slipping" into not responding and the RPM needle will jerk around; but that's in DRIVE, of course.
If you decide to try out my advice, follow this tutorial; the engine is almost identical to ours and I followed it when doing mine. The process is pretty brain dead obvious, and even if it isn't the issue, you could really benefit from it.
Sunday, June 7th, 2009 AT 1:01 AM