If the 1993 Mercury Villager runs rough when the check engine light comes on and the code reader says 34 and 51, there is a problem with an oxygen sensor and the MAP (Manifold Absolute Pressure) sensor. Both parts together will cost around $200.
Check the codes with an OBD2 scan tool.
Plug in a scan tool.
take it to auto zone and ask them to check and then clear the codes or remove the positive battery cable and press the brake pedal for 30 seconds.
If the o2 sensor is bad, replace it. If the sensors are activating the check engine light, then the codes should be checked. The catalytic converter could be blocked or the engine may not be running properly.
There are many, many things that can cause the MIL to light up. You will need to have the problem diagnosed by first reading the codes and going from there.
Try this link, ! http://www.extreme-check-engine-light-codes.com/Ford%20OBD1%20Decoder.htm
Error codes on a 1997 Mercury Villager can be found by connecting an OBDII code reader to the diagnostic port. The service manual has a full list of error codes and their causes.
Perhaps there are no codes set to read.
Disconnect the battery and wait about five minutes.
Not without a specialized scan tool.
This can be done with a scan tool or by unhooking the battery for a minute.
most auto parts stores do it for free