I have a 04 with about 184,000 on it. I recently had my front two o2 sensors replace because I was throwing a code for incomplete circuit on the passenger side. They were original and I figured needed to be changed anyways. That took care of the code. I also had horrible acceleration, with really bad bogging down and rough idle. Sometimes it would die at idle, especially if you just tapped the gas a little. I still have the idle problem, all others have been resolved by the o2 sensors replace. The mechanic did say that my back two sensors need to be replaced, will they effect by engine performance?

 

Some people say the downstream O2's have no influence on performance, other people say they do. I've read a few places that Ford says they only have about 3-5% influence on what the PCM does.
Personally, I would try other things first. If your plugs are old, replace them and the COP boots. Clean your throttle body and mass airflow sensor, and check for vacuum leaks. Those are the most common issues I've seen.

 

What's the easiest way to clean the throttle body and check for vacuum leaks?

 

Throttle body - remove the air cleaner tube, unplug the wire harness to the throttle body, remove its 4 bolts. Use throttle body cleaner (not carb cleaner; it removes the protective film on the throttle body plate). Clean the round plate good (front and back). Re-install.


Vacuum leaks - check all hoses at and around the intake (source) to destination connectors. If in doubt as to the hose connection, replace them.

 

184K mileage ...when was the last tune-up ?

 

I had new plugs at around 120,000. It runs fine as long as I'm not idling. I have noticed that when idling the ac hardly works at all and picks back up when I accelerate. When turning at slow speeds, like 5-10 mph, the steering seems tight.