One problem related to engine has been reported for the 1998 Mercury Grand Marquis. The most recently reported issues are listed below.
Ltr fm louis hettinger(ky) owner of a 1998 Mercury Grand Marquis 4-door vehicle question if vehicle should be recalled because of fast idle. The iac valve was replaced on the vehicle but did not help the problem. The service dealer stated that there was nothing else they could do to resolve the issue. There were other consumers who experienced the same problem. (there was a fast idle upon start up and the vehicle would slow down at short notice. When the problem occurred, there was no way to control the vehicle).