I've done three motor swaps now in these cars, the last two worked just fine, now this one I'm having some issues. The car is a 2001 XLT with the 3.0, this time around I used a Taurus Duratec 3.0 because it was $700 cheaper. Everything seemed fine on first startup and for the first day, then I noticed it stumble, then again, then all of a sudden it was running with a really rough idle.

I don't have any codes present when I check. I've replaced the pre-cat o2 sensors, tried two different MAF sensors both of which I cleaned thoroughly, tried THREE different IAC's, cleaned every one of them. Most recently, tonight, after cleaning the third and final IAC then disconnecting the battery for a while before hooking it all back up, I thought it solved the problem. My idle was smooth and everything seemed perfect. But then it slowly started creeping back in and now it's back to where it was.

If I disconnect the IAC, then start the car and hold the throttle to about 700 RPM, it runs perfect.. Is there anything else that works with the IAC? I'm stumped on this one. Any help appreciated!

 

Also, all my o2 sensor parameters are all over the place rather than reading a steady .09 to 1.0V. The car runs great with plenty of power and what seems like a misfire completely clears up after 2k rpms.

 

Check the motor has a good earth connection to the chassis?

 

Thanks. I checked everything again this morning and it all appears fine. With the engine cold and first start of the day it ran perfect. Drove a few miles, still good, then as soon as the motor got nice and hot the problem started again. It has to be something giving it problems as soon as it enters a closed circuit once it's warm, just need to figure out what.

 

I think I would get access to an OBD-II scan tool that can display particular selected values as the engine runs and goes into closed loop. I had thought of flex-fuel injectors being substituted in the replacement engine or vice-versa, which will not work well with a computer ignorant of the change.
tom

 

Just wanted to update, It's running perfectly smooth now. It finally gave me a code, cylinder 6 misfire. Put a different coil pack on and it helped a lot but still didn't quite do it. Next I pulled the intake manifold and installed new upper and lower gaskets, new plugs, double checked the wiring harness, and ran new vacuum lines throughout since the old stuff was not in the best shape and questionable at best.

After all that I started it up and much to my disappointment, it ran worse than ever. On a hunch, I pulled the vacuum line from the top of the EGR. Instantly it ran better. There must still be an issue with the actual EGR itself, or the DPFE sensor. I plugged that line for now and it's running great, all the o2 sensors are reading as they should as well.

 

The EGR is not supposed to be active when the engine is running at idle speed. Nor, for that matter, when the vehicle is not moving.
You must have a functional EGR valve as removing the vacuum line allowed the valve to close and allow the engine to run properly.
Perhaps the hoses are connected improperly? Given that it didn't have this problem previous to all the kerfuffle, a swap could be a possible reason.
tom