Ford Repair: check engine light, intake manifold gasket, vacuum leak

Question
Clay,
 I just had an EEC test done on my 98 taurus (big 6 cyl). The codes came back PO171, PO174, and PO135?  Cost for repairs will be approx. 427.87. The check engine light has been on for about a month, and recently it has been acting like it wants to stall at red lights ect. The car has 142000 road miles and been maintained well.
  Can you tell me what those codes are and should I not drive the car until I have the repairs made?
         Thank you
               Jim

Answer
Jim, the P0135 is a code that tells us the oxygen sensor heater circuit is open on the upstream sensor for bank 1... this is the sensor in the back side of the engine exhaust manifold.  You may find it is unplugged, or that the sensor has failed.  This would not likly cause the stalling problem, but the lean codes would coincide with a stall if the vacuum leak/loss of fuel delivery is severe enough.  
The codes P0171 and P0174 are lean codes - meaning that the O2 sensors have detected that the engine is running lean, outside of the normal range.  The lean code itself would not be a reason to park the car... it could be the result of low fuel pressure, a vacuum leak, or a faulty BARO reading from the MAF sensor.  Since the code is for both cylinder banks, you would be focused on items that affect the entire engine, not just a cylinder or one bank.  Examples are:  low fuel pressure due to a clogged filter or a weak pump, plugged injectors, cracked intake manifold gasket or throttle body gasket, etc. The stalling concern may very well be linked to the lean condition.
Hope this helps...
Clay