Q&A

Those parts had actually failed over the course of two years. I guess my reason for posting them was to aid in the diagnosis here. If a code is generic (too rich) how can one really accurately diagnose this issue? I'll check with one of the Ford specialists you linked.

Thanks!

My problem is similar, including it only occuring in colder weather. The difference is my check engine light is now on.

Did you find out what was wrong? I live in a very small town, and have a great mechaninc, but I am thinking we may have the same problem..

Thanks,
Rhonda

I have 2000 Expedition 5.4L with rough idle in cold weather. This has been happening for years, only when below 28 degrees and only on idle at a stop light. Engine RPM's drop then rev back up until I accelerate. Once weather warms up it stopped. This winter, which was really brutal for Salt Lake, it started before the cold season and finally got a "check engine light'. Autozone gave me Lean Codes PO171 & PO174. The recommended fix'its are clean MAF, faulty pre-Cat O2 sensor, EGR, Fuel Filter clogged, Fuel Pump bad, vacuum leak somewhere along engine Intake Manifold...OK, the solution to my problem....I hooked up a fuel pressure gauge to test port and found that with Key On Engine Off, pump would prime to normal operating pressure, then quickly bleed off unless the vehicle was started. Sometimes even with a straight crank from off position engine would not start. With Key On Engine On fuel pressure gauge bounced around a bit instead of a smooth needle position. (pressures should be between 28 and 45 psi) while running. So, found Pressure Regulator on fuel rail. Removed snap ring and replaced. Went key on engine off, no more bleed off. Started engine and drove, problem solved. No more lean codes...........Why this was only happening during cold weather is anybody's guess, but there is a small diaphragm in the pressure regulator that, if stuck, or worse yet a bad or torn seal exacerbated by the cold air....dunno...
Please Please............

1. Be careful what you act upon after reading on internet. There are lots of well meaning people like me but there is lots of bad information. My fix here may not be your problem. The pressure regulator is not named as a culprit with the Lean Codes I mentioned.

2. O2 sensors get a lot of blame, so do MAF,spark plugs, injectors and the like. Autozone is famous for giving generic information for Engine Codes with lots of "possible" fixes. Once you do those fixes you can be well past what a mechanic would charge..All good for Autozone and bad for us...I even called Larry Miller Ford and spoke with a Service Advisor. He told me I had a bad "check valve" on the pump....no such thing LOL, "check valve" is the regulator.... Nice Huh...Hope this helps...Reply back if you ever found out your problem...

Since I posted the original question I had to replace the intake manifold due to a crack that occurred. It was in the middle of summer and the car would barely run - very rough idle all of a sudden. The repair was quite expensive, but it was cheaper than buying another used car - about $1,800 for manifold, coils and a few other items that needed replacing at 185,000 miles. After replacing the intake manifold we haven't had one issue with rough idle in cold weather - completely healed!!! I also noticed that the small tap-tap-tap noise that had been present since I bought the car new in 2000 was completely gone. I always thought it was a small exhaust manifold gasket leak. I think it was an intake leak that just got progressively worse over time and would only exhibit failure during cold weather when the metal parts would contract and increase the leak.

I know there are lots of different fixes for rough idle since it can be caused by dozens of part failures, but thought it might help someone else who has tried everything else.