Yep, my guess would be a vacuum leak also. Check for any cracks in your rubber vacuum hoses and any rubber caps you placed on your vacuum ports. One day I forgot to put a cap back on a small manifold port while I was testing and it did actually idle a bit higher because my engine at the time was running a little rich so it enjoyed the extra air. However, on a different day, when I was driving around the block, the plastic power brakes vacuum nipple coming off the brake booster cracked and my engine choked on all the extra air and dropped idle. So it all depends. Good luck tracking down the issue! If you find out what it was, let us know.
