I have a 2005 Taurus SE w/ 3.0 liter V6 with 68,000 miles. Within the last week, I have developed several issues. The CEL goes on for a day or two then it will go off. I took to AutoZone and it show a 300 Code, which they said was basically a misc. misfire or malfunction. They also told me it could be one of a LOT of different problems. When I first start up the vehicle, my RPM used to start out about 1400-1500 RPM. Now is between 2200-2500 RPM, then it takes a long time to drop down, sometimes too low around 500-600 RPM, almost to a point where it feels as though it will stall. Once the engine is warm the idle is rough and the RPM gauge fluctuates between about 700-850 without the compressor running. Also, when I drive down the street at a steady rate, the car is surging a bit and the RPMs are not steady. On the freeway going about 60 mph, the RPM use to be about 2000. Now it is between 2200-2300. I'm disabled and unable to afford to take to FORD(charge $80 to put on computer). Any suggestions of something I could do to rectify my situation.
There's a couple of common failure items that could be causing all this:
The first one would be a vac leak around the intake air control valve (check out the topic finder, '04-up vulcan engine poor idle, hard start). It's on the back pass side of the plastic upper intake manifold, round in shape, has a wire harness with 2 wires going into it. The o-ring gasket at the seam is prone to leak, it's a easy fix if you remove the pass side cowl. You can check for vac leaks with starting fluid, but only do this when the engine is cold, as starting fluid is combustable. Use a rag to wipe up.
Another common vac leak is the pcv valve hose, see the topic finder on the how-to on that item.
The second issue could be your car needs a software update to correct the erratic hot idle issue. I was going to take my '07 Taurus into the dealer to have this done, but I traded the car in for a new one instead.