Momentary Hiss upon Acceleration, among other things.

[cwackduck]

Hey guys!
This is my first time posting, but I VERY commonly come to this board when I have any kind of problems with my Ranger, and it's always been super helpful. I'm not super mechanical, but I'm a big do-it-yourselfer, and I need some help getting on the right path here, I think.

Within the last 2 months, my Ranger has started acting up and getting REALLY crappy gas mileage. I've tallied it up and it's getting somewhere around 11mpg. Prior to this it was getting about the average mpg and I haven't had much trouble with it. I've started a new job where I typically drive about 50 miles a day and the cost of the gas is starting to add up...

For starters, I have a 2002 Fx4, 4.0L v6, 31x10.50x15 and JUST rolled over to 149k on the odometer.
What's going on with the truck: Other than the bad mileage (which I'm assuming is a result of the problem) at around 35 - 45mph, the truck shakes like I'm driving on a gravel road. Typically it's when I'm in a slow zone where I have to just keep ~40mph. It almost feels like the truck is jerking-foward, not pulling smoothly. It happens a little when cold, but seems to be more noticeable when it's warmed up. At highway speeds it seems to go away, or at least be a little less shaky. It also idles rougher than I ever remember.

Since this has happened I've googled the hell out of the issue and visited this forum for answers. Here's what I've done so far:
All new plugs and wires, cleaned the MAF, put in a new PCV valve, replaced fuel filter, replaced the transmission mount, and yesterday cleaned out the IAC. Each helped a little but didn't fix the problem. The truck idles a lot quieter since cleaning the IAC (which was pretty dirty), but still idles rough at ~800rpm at rest. I've checked all of the vacuum lines (and elbows) I can think of and couldn't find any cracks. Also, the vacuum ball is still in one piece, and I haven't modified anything on the truck.
It was after cleaning the IAC that I noticed my truck making a hissing noise right when the throttle is pushed in that I hadn't noticed before. It seems to be coming from behind the throttle body area I think. I made a video of this that can be watched here: http://www.youtube.com/watch?v=-Vp_gHKPS_U

At this point I'm thinking it's got to be a vacuum leak SOMEWHERE in this thing, but I'm not 100% where yet. When I get a little more confident and have a fire extinguisher handy, I'm thinkin of trying the "carb cleaner test" around the engine to find any hidden leaks that way.

So, from this short novel I've written here, does anyone have any other suggestions for anything that I can try that I'm obviously overlooking here?
I'd appreciate it!

Edit:
Also, one thing I forgot to add. Before I cleaned the IAC, I "tested" it but unplugging it while the engine was idling. I'd read on here that it was one way to test if it was working. Some said if it was working, the idle would get REALLY bad, but in my case, the engine shut off entirely and wouldn't start without the IAC plugged in. Dunno if this is relevant or not, but just thought I'd throw it on here.

 

[sholzy]

Since you did all that work, you need to reset your computer and drive it so it can re-learn things after the cleaning. After you've driven it, you need to pull the codes so we know exactly whats going on. Most auto parts stores can read the codes for free. Sometimes after cleaning the MAF, IAC, and once the computer re-learns things it might smooth out and run good.

The hissing sounds like a vacuum leak. Look near the back of the manifold on the driver side. You will see a fitting sticking out the side with several hose connectors. Sometimes a hose will come off and the manifold will suck air. With the engine running feel around that fitting for the vacuum leak and look for the hose that is either cracked or off. You should hear the difference in sound when your hand moves across the leak.

 

[cwackduck]

Hmm, I haven't reset it yet, the battery hasn't been unplugged since I cleaned the MAF sensor a couple weeks back.
I'll go do that and let it drain out a while.
I'll have to poke around for the leak later, it's kind of what I was suspecting when I heard that noise.
Another thing, if I haven't been getting the CEL, or anything else, will it still be putting out codes?

Thanks for the reply!

 

[Yellowsplash]

If you look on the passenger side valve cover towards the front of the vehicle there is a rubber elbow thats part of the crankcase ventilation system. It runs behind the engine to the drivers side. The elbow is a VERY common issue on the SOHC engines, as it either collapses or splits open allowing a huge vacuum leak. I would inspect all these rubber connectors and make sure theyre okay. I cant tell you how many of these I have replaced.

 

[cwackduck]

Hey guys,
So I reset it last night. It made some awful noises for a little bit until it got everything back under control, but then is evened out. It really seems like it's running pretty close to how it should, there just seems to be something off. It idles in the right areas (1200 - 1100rpm on start, then settles at 800rpm after a short time) and in general is a lot quieter than it has been in a while.

I've checked that elbow a couple times already, and the line running back to the pcv, but it seems like it's still good. As often as I'd read about that being the culprit I keep checking it just to make sure I'm not missing something.
When I put my ear up around the area, I do hear what could be a leak, but I can't nail where it's coming from. Seems like it's more towards the back top area.

I'm to the point where I wanna use the carb cleaner to check for leaks, but I just wanna make sure I don't burn my truck down in the process. Is there anything I should specifically avoid getting the cleaner on? And should I do it while the engine's cold, or can I do it after it's warmed up?

 

[Big Jim M]

Howdy Duck. If it is idleing at 800 it's doubtful there is a vac leak. HOWEVER.. What I use is a small torch tank of propane.. You know the small ones.. I open the valve and don't light it. Then with the engine running I move the torch end around next to all the places that there might be a vac leak.. If there is a leak it will suck in the propane and the rpm will surge.. easypeesy! And the carb cleaner isn't taking the paint off of my engine.
There is no danger as all that happens is the fan wind blows the propane away and mixes it with so much h2o that it can't burn anyway..
Big JIm

 

[cwackduck]

Well, rather than letting this be another unanswered forum question, I figured I'd give a bit of an update.
So I've been fiddling with it lately to no avail. Nothing major, just little tweaks and tests. I did get out the propane torch and wave it around but never heard any surges. When it gets a bit warmer and I can stand to be outside, I'll get an extension hose on the propane and really get it in the nooks and crannies for a better test.
Fast forward to this past Saturday when my friend and I are outside taking a look at the throttle body. I have him go around and start the truck while I'm staring at it, and I say to him "Ya know, it has all the symptoms of a vacuum leak and everyone says to look at this elbow joint here, but I've checked it a thousand times and... oh sh*t, look at that."
And right in front of my eyes the elbow valve gets vacuumed shut and collapses when the engine had been running for just a short time.
Now, for some reason I had only been looking for a HOLE in the thing, and when people said "collapse" it never actually clicked in my head that it meant the hose was pinching shut and choking the system.
And for some reason, I guess I'd never really looked at it enough while the engine was running to notice it was collapsed, I was always looking somewhere else.
So Sunday I went to autozone and bought myself a plastic 90 degree PCV elbow and radiator hose and made myself a new elbow and suddenly it's like my truck gained 3 extra cylinders. It no longer pusses out going up hills, doesn't surge at 40mph like it did before, and even my brake pedal seems to be less spongey.
I do plan on getting an actual elbow replacement, but until then my little hackjob is functioning well enough.
The throttle is still hissing like in the youtube video I linked earlier, and it still shakes a little more than I think it should when idling, but it's running well enough now that it can wait until warmer weather!

Thanks guys, for the suggestions, and thanks YellowSplash for continuing to hammer the ventilation elbow idea into the heads of dummies like me.

When I do get around to the rest of the issues, I'll update on here to hopefully help some other sap having the same issues!

 

[Yellowsplash]

Im glad you finally found it...I'd go ahead and reset the computer too so that the fuel trims reset and will relearn faster. Might find it to run even better...