Hey Everyone, long time lurker/new member here. This morning I pulled the fuel rail off the truck. While off, I put on a new fuel pressure regulator and changed the O rings on all the fuel injectors. After some more cleaning, I buttoned it all up and started it up. It's running like poop! Starts with a high idle that comes down to normal after a minute. Sounds like its going to stall out. Turning on the AC made the idle drop more and felt it almost stalled. It threw the P1151 code. All the O2 sensors are less than a year old . I don't know if its worth mentioning that I put a new Bosch fuel pump and Motorcraft fuel filter on last week. Any input is appreciated. Well I'm off to buy a bus pass for tomorrow

 

I forgot to mention that I was not having any issue with the O2 sensors prior to today. I was trying to take care of a long crank/ low starting pressure problem hence the pump and filter change last week. New plugs, wires, air filter, MAF cleaned.

 

Several things so please don't get insulted because you need to learn.
First the 1151 code is not the OX sensor.
The OX sensor detects the fault that is an air leak somewhere in the intake system likely from your work.
Check out the mass air hoses connections, any gaskets or intake areas you had apart.
.
The air leak is adding air to a 'normal' high idle for cold starts.
The idle coming down after warm up is also normal.
The A/C load should be automatically accounted for by the computer opening the IAC a bit more so the added load should be transparent to you.
Find the air leak, repair then see how it works out.
.
Here is how cold start works.
The computer samples the resistance values of the coolant sensor and the intake air sensor. This is the only way it knows it's to be a cold start.
These set the IAC open for high idle, advance the ignition timing and increase fuel injection amounts.
After starting, the OX sensors have to heat to at least 600 degree to begin outputting their signals back to the computer. This usually happens within the first minute.
When this happens the higher idle comes down to normal providing there is no fault in the hardware control system.
.
Equipped with how it works and how it acts, you can begin to trace the issue.
Good luck.

 

Much thanks for the advice. And no worries, I don't get insulted when I'm explained something by someone who knows a heck of a lot more about it than I do. I didn't smell gas so I'm sure the fuel system is buttoned up well. I grabbed my flashlight and did a closer inspection a few minutes ago and saw part of the intake gasket that isn't supposed to be showing. Looks like there is my leak. Well, first thing in the morning I'm going to open up the intake again and make the needed adjustments.

Thanks again for the info. I'll give an update tomorrow on how it turns out

 

P1131/1151 DTCs may indeed be caused by faulty O2 sensors (see PCED). Failed or "lazy" O2 sensors will do this.

However, in this instance, it's likely an issue with excessive un-metered air or insufficient fuel on bank 2 as a result of something not going together quite right.

If you have a scan tool that can monitor either the STFT or the O2 sensor voltage, pull that up and hit the suspect area with something like carb cleaner, brake cleaner, ether, or even propane while watching the display. If you see a big change in the monitored parameter, you've found the vacuum leak.

 

Well Gents, here is the update. Pulled open the intake, CAREFULLY placed everything back together. Payed VERY close attention to torquing things down to spec. Realized that I also had two of the plug wires wrong on the coil pack. On start up, things seem back to normal. Hopefully this issue is resolved. Thanks for tips guys!