cant keep 1998 mercury marquis running, it'll start and run if i Feather the pedal, once released stalls out.
If it runs rough then I'd say check sparkplugs. If it's smooth it might just need to have the idle increased by a mechanic (or yourself if you know how)
check for a vacuum leak at the motor. or the idle air control valve. idle is set by the pcm on that vehicle and cannot be adjusted.
As said, check the idle air control valve. If its not working, it wont let the engine idle, with your foot off the throttle.
Looking for a Used Grand Marquis in your area?
CarGurus has 1,536 nationwide Grand Marquis listings starting at $995.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts
Related Models For Sale
Used Cars For Sale