I have a 2000 Mercury Marquis 4.6L owned since new by my family. Only has a little over 30k miles on it. Was running perfectly until Saturday night. Haven't used it since earlier in the week. It starts but won't idle for some reason now. The only way to keep it running is to hold the gas pedal down a little but when you let it off it dies. Have 3/4 of a tank of gas. Don't see any codes shown on the dash but as I said the car won't idle. Any ideas as to what I should look for. I do have a OBDII Code reader I am going to hook it up tomorrow morning and see if it will pickup any codes not shown in the dash. In the mean time I am stumped.

 

Found the problem on my own this weekend. Ended up being the Idle Air Control Valve. Ordered a new one online and should be here in a few days.