Ok. First off thanks in advance. I have been reading and reading on these issues on here for some time. I have found alot of great information.

Last winter when the temps dipped very low I got the dreaded P0701 and P0704 codes along with a rough idle in my truck. Did some searching on here...Cleaned the MAF and replaced the PCV valve (motorcraft) and hose assembly. Check engine light went away, no more issues until this winter.

My issues pop up when the temp dips below 10. Unfortunately we have had plenty of that lately. I'm getting a rough idle. The same 2 codes have popped back up. There have been 3 times when the weather has been below 5 that I have noticed a whistle while driving. It typically shows itself when the RPM's are in the neighborhood of 1550. If I accelerate or decelerate this goes away. So, I've got a vacuum leak to pinpoint and haven't been able to do so yet.

Also along with this I have the rough idle. The colder it is the worse the symptoms. This morning we were below -10 and my idle under load was dipping low (~500) and jumping around. I noticed similar symptoms on my way home. When I pulled in my drive I put the truck in neutral and the RPM's were jumping around between 600-800.

So, I have a vacuum leak. Is that causing my idle to jump all over? Or do I have an IAC that is sticking as well? Or is there something else that is popping out to one of you with far more knowledge than I? Any suggestions on where to start? Thank!

 

I think you mistyped the codes - those are transmission codes.

It's easy enough to pull the IAC and clean it - use WD-40.

 

You're correct. Sorry! Was in a hurry and going off memory.

Codes were P0171 and P0174.

Will do on the IAC...Thanks.

 

Lean both sides and a whistle - that's definitely a vacuum leak or an air leak in the intake tube after the MAF.

 

Ok, so I pulled the IAC last night and cleaned it up with some deep creep. This morning the truck didn't seem to have quite as erratic of an idle. So, I'm guessing that is one of my issues.

As for the vacuum leak...I have a couple of questions. I have been trying to take in as much information as possible on this topic through the search function. I have seen it mentioned a couple of times to dip the ends of you vacuum hoses in lacquer thinner before placing it over the fitting to ensure a good seal. Does this include things such as the elbow on the back of the PCV assembly? Also, is there a common spot where the intake tubes leak eventually?

I did some looking last night while I was under the hood and for the most part my vac hoses look really good. I haven't had a chance to test them individually yet. Hoping to do so this weekend. I'm just trying to overwhelm myself with information between now and then to make sure I cover all my bases!

 

If you hear a whistle, it's more than just a minor vacuum leak on a small hose at the fitting. You shouldn't need to use lacquer thinner.

The PCV elbow at the back of the throttle body is the most likely issue - it rots and cracks. Other items to examine carefully are the intake tube itself between the MAF and throttle body. Check the brake booster hose and the evap purge hose.

 

FWIW, I'm having the same exact issue. Same codes. And it only happens when it's really cold. My problem is that it showed up when our temps dipped into the teens every night for a few days. My mileage dropped to single digits then, too. But it has warmed back up, and the problem has disappeared. So now I'm having trouble finding the leak. I don't want to wait until it's that cold to look, because, well, it's too cold to be out there, lol.

So my question is, where are the most common leak points? The PCV elbow and intake tube have been mentioned. Are there others I should look for that fail more frequently? I plan to just replace hoses and see if the problem goes away. Then again, with 160k miles, maybe I should just replace them all.

 

You need to clean the entire PCV system out. Make sure you using a Motorcraft PCV valve (very important). Clean the IAC again, but clean it @ room temp or just warm it up a bit.

If you have compressed air, you can clean it right. Shot of break cleaner, - blow it out, move the internals by hand (plunger), then DeepCreep and move the plunger to work it in. Blow it out.

Check you PCV system for cracks and holes. The engine won't be able to breath properly without a Motorcraft PCV valve. Once everything is cleaned up checked and replaced, take the vehicle for a long drive to burn all that moisture that's collected under the valve covers, - which is blowby.


skell : No lacquer thinner, - regular paint thinner w/MEK. Read this, -

https://www.f150online.com/forums/5051380-post7.html

 

Had a similar issue on my 01 Expd. Replaced teh IAc, and PCV along with all associated plumbing. Ended up being a cracked intake manifold.

 

Thank for the info. I'm going to be going checking all this out tomorrow.
The PCV hose/elbow were new at the beginning of last year. I will of course double check them this weekend, but I'm hoping it didn't fail that quickly. The PCV valve itself is new as of 2/3 weeks ago. And it is a motorcraft valve.
jbrew - when you say clean the PCV system, are you refering to just the valve and hose assembly? And what is an ok cleaner for the job?
I'll pull the IAC again and clean it as you suggest. It certainly wasn't at room temp when I did it the other night and I maybe wasn't as thorough in the cleaning as I should have been. And I did realize I misspoke about the lacquer thinner while doing further research...thank you for the correction.

I'm going to check all vacuum lines first and foremost. In all my research, I'm also discovering that intake manifold gaskets or the manifold itself seems to be a common issue. I realize I may be getting ahead of myself a little, but is there a way to check this to verify whether or not they are the source of my vacuum leak? I haven't seemed to find much of a procedure for this other than propane/spraying something along the gasket.

 

Glen - How did you figure out that's what the issue was?

 

Regarding sleuthing out vacuum leaks, I've read of people using smoke injected into the intake or vacuum lines to look for leaks. This seems far safer than spraying combustible gas around a running engine. I assume the smoke test is with the engine off. Automotive diagnostic smoke generators are expensive, but I found someone who will lend me a cheap homeowner grade one that might work. I'll let you know what I find, if I go that route.

 

The Ford dealer smoke checked it. they really had to get the nozzle down in the nooks and crannies to get any results.

 

Update: I got under the hood this weekend to check everything out. Did the following...

- examined all vacuum lines.
- examined air intake
- cleaned MAF sensor
- replaced rubber portions of EGR line
- cleaned IAC valve as directed by jbrew

I did not clean the PCV system as I was unsure as to which cleaner is ok for this. I did pull the PCV assembly off and inspect it and it looks like new.
The rubber elbow and piece of hose on the EGR line were cracking and the exterior was disintegrating. I could not locate any spots were there was a hole all the way through however. If those were the culprit, would there be a noticeable hole for there to be an intermittent whistle?
I haven't put much for miles on since doing all this, so time will tell. I am not very confident that the EGR rubber is my problem, but it has been updated regardless.
I did discover while under the hood that I also have a very small coolant leak at the hose connection to the heater core. Which after searching on here seems to be fairly common. So if it comes down to me replacing intake manifold and/or gaskets, I guess it would at least make it easier to repair that issue at the same time!

 

Leaks at the heater core connection are about impossible, - unless you stuck it with something. Still it would be VERY hard to do.
On the engine side, yea, the hoses are clamped and wear from the inside out at the connections.

Soap and water on the PCV system, - just wash it in the sink while mama has her head turned. Then blow it out w/compressed air. Then check it or chuck it.