1 have 2001 mercury it will not idle

there,s not enough information provided for a good answer here,,you did not say what kind of mercury,,or the engine size.

if it runs ok other than at idle l would suspect either vacuum leak or a bad idle air control valve. sometimes a little tap on the iac valve will unstick it. if it does that is the problem

Hi Speed, quite a little info on this, you can check for a vaccum leak or cracked rubber lines.
Have you checked the ''Jack'' valve???.
Good luck!!!.

Start by cleaning the throttle body. They fill up with carbon and block off the feed port for the idle circiut. Second do a check on the idle spped motor with a scan tool to see if the pintle is moving when prompted too. If not, replace it.

vaccum leak or the idle control sol.

The IAC ( idle air control ) valve is stuck. Replace it and this will solve the problem. l have seen this many many times.