97 astro vibration when started

this morning i went to start my van and while it started, it started vibrating really hard and then the service engine light came on. needless to say, i was afraid to drive it. i went back out later and while the vibrating isn't as bad, and then is tapering off the service engine light remains on. we had to replace the idle arms and the air compressor last year--any ideas what this new problem could be? many thanks.