~ 2 weeks ago:
I had gotten P0171 and P0174 codes and truck ran fine. I did a real quick check for loose hose connections, etc and then for grins, cleaned the MAFS. The SEL went out on it's own after about 70 miles of driving or so. I was surprised.

~ 400 miles later:
The truck starts shuddering/missing (not sure what to call it) at low idle. Really rough idle. It does the same with any light acceleration. Whether 35mph and lightly accelerate or going 60mph and lightly accelerate the rough "shudder/missing" is there. But if I go ahead and get on it a bit, the shudder/roughness eases off significantly but you can tell it's still there. I don't really recognize any power loss once I get on the gas.
Here is the sequence of events regarding codes:
1. P0171, P0174 ran it with these codes for about 250 miles.
2. Cleaned MAFS. SES light remained for ~70 miles then went out.
3. 400 miles later shuddering with no SES light but scanner detected P0171 (no P0174).
4. Drove it about 20 miles (not by choice but had to). SES Light with following codes: P0171, P0174, P0308, P0316

Before I jump on the P0308 with a COP, could whatever is causing the P0171/0174 have caused the P0308 to trigger since those have been the most prevalent?

Thanks.

 

BTW, anyone order from "Motorcraft" on Amazon? They are selling the DG508 COPs for $38.
Wondering if these really are Motorcraft COPs. Folks in the reviews are saying the packaging has no markings.

 

You need to look for vacuum leaks. The prime place to check is the PCV elbow behind the intake, it cracks and rots out.

Are you sure you aren't due for spark plugs?

Rockauto.com has Motorcraft cops for $41.79 each, Delphi cops for $32.79 each, and Denso cops for $22.89 each, they are just as good. It's expensive, but I'd recommend you replace them all rather than just one at a time.

 

After reading some more posts I went out and grabbed some freeze frame data. This was with the truck off...not sure my scanner can do this with the truck running.
Calc Load 20.7
STFT1 7.0
STFT2 9.3
LTFT1 24.2
LTFT2 22.6
RPM 686
Coolant 165

I know nothing about these fuel trim levels and haven't found much on what they should be. I did find that close to 25% on LT Fuel Trim tends to indicate vac leak.

I saw a pretty good video of someone explaining vac leaks and they used a spray bottle and sprayed water all over the place to find theirs. Is that safe for the engine?

=== Edit after seeing GLCs Post above ===
Plugs have 68K miles on them; Truck has 180K miles on it.
Note that the problem doesn't seem to manifest until the truck gets warmed up a bit. Based on only the 3 times I've driven it since the problem arose.

Thanks.

 

The PCV elbow. Main source of these problems. Follow the PCV line to the back of the throttle body where it attaches to the intake 9 time out of 10 thats the problem.

 

And with 68k it wouldn't hurt to change the plugs, especially if they are not Motorcraft.

 

Problems seems to be fixed. Appears that I had a vacuum leak and a bad COP.
After checking hoses again...this time in the daylight I found a crack in the rubber fitting that connects the PCV line to the throttle body PCV tree(???). I have the coolant heated PCV setup.


After wiggling it a bit, it looked like this.


I replaced just the cracked rubber piece with a piece of fuel line hose. No visible difference in performance. Truck still shuddered with acceleration. I replaced the #8 COP and boot based on the P0308 code. Shudder gone and all codes still gone after ~120 miles.

Question: Do you think the vacuum leak and the bad COP were a coincidence or could have the vacuum leak led to the bad COP. Note that the SES light for the P0171/P0174 was out for about 400 miles after cleaning MAFS before the P0308 and shudder started.

 

Those r lean codes che k the hose going to your pcv valve also check the airflow hoses coming from the egg valve

 

Sorry EGR valve

 

Marc, it's fixed.

To the OP - it's coincidence.

 

Comments on spraying water around potential vacuum leak areas to identify leaks?
I saw several youtube videos of people doing this. Is this safe for the engine?

Thanks,

 

In my opinion I should be just not waccumulous amounts before drying like anything else that won't burn t will evap

 

???????????

In English, please?

 

Crud. Couple hundred more miles and now the P0171 is back.
Guess I'll look into getting a small propane torch and try that to check for leaks.