I have a 2005 f150 with the 5.4 and it randomly started a rough idle and running very rich to the point it's smoking from the tail pipe and smells like raw gas. It is also very sluggish and almost no response until I hit 2000rpms and it then feels like I hit nitrous and begins to accelerate normal as long as I keep the rpms up higher. I get the codes p2198 p2196 p0454 and p0175. I've replaced the MAF, oxygen sensors, plugs, checked injectors and no leaks with multiple key cycles. Brought it to the ford dealer and they told me I had low compression and that's what was causing it but low compression would make it run bad all the time and from time to time it'll run good for a few days. Any input is very much appreciated.

 

I feel your pain! My 05 (5.4l) was diagnosed as having low compression in cylinders 6,7 & 8...

Mine runs rough at times...and perfect at times...I think mine may be vacuum related, but I haven't been able to track it down...

My truck shows running rich on one side, and lean on the other (but not so much as to give a code)...I continue to drive it...it gives no codes, and doesn't stall...been this way for 15 months now...

It also seems that when the temperatures are above 80, and below 60, or damp outside it runs the best...

Seems to be a common problem as these age...I am at 189,400 miles...

 

Running rich could wash the oil off the cylinder walls and cause low compression because of excessive wear on the rings and cylinders. I suggest you make double darn sure your injectors aren't leaking since that tends to be a problem with 05's.

 

I removed both sides of the rails off and had someone cycle the key multiple times while I checked the injectors and I couldn't see one single drip. I'm starting to think it might possibly be the fuel rail pressure sensor?