Idles low about 600 rpm in gear at a complete stop. changed the cam sensor and still idles low.
P0171 is a lean code for bank 1 sensor 1, it has nothing to do with a cam sensor, things you need to check: air filter, fuel filter, fuel pressure and flow, vacuum leaks, ie PCV valve, intake leak, and of course the O2 sensor itself.
check also intake air control valve. If it runs good with your foot on the gas pedal but runs like s*** with your foot off the gas pedal start there.
Search Mercury Montego Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Mercury Montego Experts