It takes two drive cycles for the code to set again. I vac leak at the intake gaskets would be more prevalent in colder weather on first start up.....Does the engine seem to idle higher on the colder mornings? I still wouldn't rule out something simple either like a vac line or fitting....

 

No, it doesn't idle high at all. If it wasn't for the check engine light I wouldn't know that anything was wrong. Is the best way to search for a vac leak to just listen or is there another method that would be suggested?

 

I use I little tank of propane for vac leak detection.

What is your IDLE @ exactly?

You have an 05 5.4L correct ? Did you try a full reset ? With only 39,000 miles and the PCM being a little flaky IMO on the 3 valve, I would disconnect the battery (both sides) for 15 minutes or so and reconnect for a reboot.

It's free and worth a shot.

 

What I have done in the past looking for vacuum leaks is use Gumout sprayed around the bases, seams and fittings. Any change in RPM's would be a possible source for air being sucked into the engine. For air blowing out you can try a spray bottle filled with a mixture of water and a few drops of dish soap. Same thing you do for locating a tire leak.

John

 

First post states a 04 5.4 supercrew...is it the Heritage body style or the new one?

 

it is the new body style.

 

On cold starts the engine starts to idle at about 1200-1300 RPMs and after about 10-15 seconds drops to 700-800 RPMs

 

That sounds completely normal to me.

 

Yeah that does sound about right GLC...
I have yet to replace a set of intake gaskets on the new 3v motors. Your mileage seems a little low for you to be having troubles there. Only big trouble we have seen is where the vac line for the brake booster pops off and causes a leak at the bottom of the intake. You would loose all power assist if that was your trouble though and it wouln't be random. Most of the PCV system are all hard plastic lines with quick connects too, we haven't seen any troubles with those yet either. You could double check to make sure the hard plastic lines on both sides of the intake are securely snapped down.

It would be nice to know what the fuel trims were at...it has to be above 25% I believe to set the code, It would be interesting to see what the other bank was doing. Are any of the auto parts store scanners capable of pulling the freeze frame data or are most of them just generic OBDII code readers?

 

You may have to take it to the dealer and get advanced diags done.