I have a Ford Taurus 3.0 V6 with DOHC motor. I'm having extreme difficulties witht he idle on the car. In Open Mode (Cold idle) the car run extremely rough. But when the car gets up to temperature and the Oxygen sensors are operating in Closed mode the car runs better but still rough. But in both instances the car is running extremely Lean. I've check for vacuum leaks, EGR valve. I've cleaned the MAF sensor and the Idle Air Control valve. I only get the two system codes (P0171 & P0174), that the car is running lean on both banks. Even when the car is running, it still running a tad on the lean side, but at higher RPMS the oxygen sensors seem to be able to make up the difference. I have check the reading of the MAF and at a hot idle its reading approximately 3.09 gm/s, which is just slightley outside the Ford reference values for the 4 valve motor (3.4-4 g/s) and at 2500 rpm its in the range 16 g/s, and the spec values are 13-14 g/s. Since these are Reference values, I'm not extremely far off these values. But in an idle, the both the oxygen sensors(1.1 and 2.1) are showing almost 0 volts (extremely lean). Then if I remove the connector off the MAF sensor the car will start to idle little rich. Also when you crank the car up and its cold, the car will idle pretty high to start with( 2000 rpms) and then slowly drop down to the 1000~700 range. Also the Idle control valve seems to make alot of noise (whistling). I know it suppose to allow vacuum out of the Intake. I can't remember ever hearing it before, but that don't mean anything. I know that the car will imediately stall if the sensor is disconnected.
If I'm was a betting person I would say that the MAF sensor is at fault, since this seems the a common Ford problem. The car runs fine from a drivers prespective, when driving. Just has a nack for stalling at a red light, or at any complete stop for a period of time(doesn't just stall, it takes it a few minutes until it get to this point.).
I'm curious if anyone else has had the issue. I'm almost to the Trial and Error point. But the only problem is they normally do not allow you to carry back sensors.
The measurement above are from a OBDII laptop interface. Its not a top of the line model, but one that will work with just about any model car. And the reference values come from the Ford Technical Service Publication.
Thanks, Justin Woodman