After not driving my wagon for a couple weeks, I drove to store and on return trip it suddenly lost power, with a loud whirring sound. I had to press hard on the gas to get it to drive 30-40 mph and at traffic lights it would stall on idle if not for keeping foot on gas pedal.

It stalled a couple times on the 1-mile drive back home. Once there, I opened the hood to find the engine shaking like I was going over the worst jungle road, vibrating the whole car.

The engine turns over and starts but only by giving it a lot of gas when I turn the key.

It's a 1988 240DL with 185,000+ miles on it. I changed the oil (which was needed). I'm new to the fix-it-yourself world and would like to puzzle this out without going to the shop (esp since I'm a student).

Any ideas?