Making me crazy!!

[Ledphoot]

ok short of it is this 94 ranger auto 2wd 3.0 124k mi. No mods except muffler. Idles rough as a cob, runs pretty good, accelerates well . checked DPFE, cleaned IAC,EGR.PCV, all check good no codes. Cleaned MAF, new plugs, cap, wires, sprayed carb cleaner all over intake, around all the vacuum hoses, check wiring plugs, pulled each plug wire to see if I could chase it to one cyl but all are even 120-115psi comp all cylinders, no comp leak down, no coolant loss, no steam, no bubbles in radiator, cleaned throttle body, new air filter, checked intake hoses for leaks, checked dipstick tube for vacuum loss. All ok. Here is where it blows my mind. I can unplug the hose from the pass side Valve cover to the air intake tube and plug it off so no vacuum is pulling from the air intake and it smooth's out damn near perfect drives great idles good for a 3.0 ??? WHAT CAN THIS BE?? Is it possible that my MAF isn't signaling properly and this "patch" is getting the tune back in step? Otherwise I am baffled. I got a steal on this clean little truck because the guy gave up trying to figure it out and didn't want to pay a shop to do it then got in a bind and needed some $$. No Codes at all which also blows my mind.. no smoke, no raw gas smell. Thanks for any and all help. This is gonna be my Rat Rod shop parts getter and my haul garden crap to keep the wife happy truck and I really would like to whip it!

 

[RideFord94]

The 3.0 is known for its rough idle. Everything youve done seems to be good. What kind of plugs did you put in it? The compression is a little low but still alright. I would also clean/replace the upstream oxygen sensors. Get a drop in filter or go for a cheap cai. A fuel filter replacement seems to be in order. You might also want to make plans to replace the timing setup. Mine had skipped a tooth and had ridiculous slack at 190k. At this point youve done about everything you can. Dump half a can of seafoam down the vacuum hose. Put a bottle or two of lucas in the tank and youre truly done.

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[RideFord94]

Also check the coil pack for corrosion mine was shooting pretty weak sparks at 180k

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[Ledphoot]

Autolite platinum plugs, ran a bunch of seafoam through it and another can in 10gal of gas some before changing plugs. Fuel filter too. I just don't get how the vacuum is so high in this engine and blocking it off and stopping it from pulling from the breather tube has evened the idle out so much. If the coil were bad wouldn't it misfire or surge at highway speeds? I can unplug the MAF and it makes it more erratic just as it should . I unplug the IAC and it also changes tune and gets worse so they are working. I can unplug PCV and its pulling vacuum too. *scratching my head on this one..

 

[Ledphoot]

any more ideas?

 

[RonD]

Check dipstick and tube.
And oil filler cap.
Do you have any oil leaks?

Crankcase and valve cover area should be air tight, or PCV and vent tube(the one you blocked) will be getting too much air.

In fact on most 3.0l's if you remove the oil fill cap with engine idling it will die, it is because of the extra air coming in.

 

[01b3000ds]

I don't understand. How can it be a problem if the engine runs smoother?

Right. I had to think for a minute about my 93's PCV location. Regardless...

T that line into the breather tube. This will re-route blowby gasses back into the intake air stream to enrich it. You may even see a small increase in your mileage (1-2 MPG). While you're at it, open up your spark plug gap by .010" and advance your timing to compensate. That'll get you another 1-2 MPG as well. Small, "seat of the pants dyno" stuff.