What could be the cause of a rough idle while in park on a 1994 Lincoln town car?

Remove the EGR valve and clean the passages and/or clean the MAF sensor in the air intake tube (use alcohol and be VERY carefull when cleaning the two small wires). Could also be the IAC or idle air control valve. There are very nice writeups on cleaning the IAC, MAF and EGR passages in the tech section at www.lincolnsonline.com