I replaced the IAC sensor in the intake manifold on my 4.0 a couple days ago. The engine has 111K miles on it. Anyway, I noticed a film of oil on the sensor. I was suprised that oil could get so far inside and high up in the manifold. Is that normal? My PCV valve seems to be working, I don't notice any blowby. No indications of oil burning.
I'm not going to worry about it but I am curious.

 

Do not look under the hood too frequantly. Less worries.... :-)
There is oil everywhere on my engine. I wash it every week.....

 

When you turn the engine off, oil vapors begin to condense on everything they can. They get through the PCV system. They can flow through the breather tube which has no check valve and is fairly large. The MAF sensor is prone to getting contaminated by this stuff as well.

 

That's perfectly normal. I have seen luxury cars with puddles of oil in the intake manifold once the top of the manifold was removed for cleaning purpose. The oil just migrates there from the valve cover through the PCV valve. There isn't much you can do unless you can devise a good trap for it.

In fact I have seen some of these contraptions on Ebay, I am just not sure they are worth the effort. In fact, I'm certain they are not worth the effort

 

Thanks all.
I replaced the IAC under the theory that it might be causing my pinging that usually happens after a long 30 minute highway trip and the engine compartment is good and warmed up. I'm not sure I can test my theory now that the temps are lower.

 

Pinging is more likely related to a lean condition. Look for leaks in the intake manifold and vacuum leaks.

 

I would chase that path if it pinged all of the time but it only does it after a long drive. The a/c will make it worse. It never happens on my short highway trips around town. I'm convinced that a heat soaked engine compartment has something to do with it.

 

hot engine from long road trip will expand/shift gaskets and manifold alignment affecting seals. 4L is notorious for this effect. results in the wear/tear of the coolant hole seals on lower intake manifold gasket.
also causes vacuum leaks to intake.
Ford OHV V6's shake their manifold bolts loose with that tall plenum and mass on top.

there is a new design lower intake manifold gasket design from Felpro and ROL that is a 2 piece, one for each side, that allows for independent movement instead of the rigid OEM one piece.

the PCV system design on the 4L is poor, the outflow of hot combustion oil boil off gases is into the air tube near the MAF, hot MAF element soaks in oil vapor and bakes it on. especially bad in a worn engine with blowby.

try a full synthetic oil such as Penzoil Platinum, Amsoil, Redline or Royal Purple, has less volatiles to boil off and coat the MAF

or move the PCV line that enters near the MAF and move it to the front side of the throttle body
another course of action is to add an oil capture bottle to the PCV line

look for old vacuum lines that soften as they heat up

i would imagine your engine is carboned up also in the combustion chambers, pre lean burn design heads are the worst, 96 and prior Aero 4Ls

pull the octane plug for 3>6 degrees of base timing retard to protect the engine until you find the cause

 

I replaced my IAC on my '93, after trying to clean the original, with no luck...it had a teeny bit of oil on it, and the engine did not 'use' oil...so this condition you have noted is probably the norm--you want to see oily deposits? Look in an intake manifold of a turbo-diesel after 200, 000 mi., like mine-it is so bad i could NOT find a shop that would let me run it in their hot-tank, and that condition is also the norm.
(they all said it ruins the water-based solvents they use)
But, the above post from 96-4wd, is the kind of advice you cannot get just anywhere,
I would follow all those suggestions.
(love that trick about the octane pin!)

 

Nearly new (about 3 years) Mercedes Actros with 12L V6. If there is leak from intercooler, there are puddles of oil near intercooler damage. It is normal.

 

Dang 96. If this wasn't an Aero I wouldn't hesitate to yank the intake. There's just no freaking room to work. I may just have to run the plus grade for now. Someday I need to tear into it and fix the oil leak(s) and this problem if it still exists.

 

with an air ratchet, it's not a bad job
have both reg. and deep sockets in metric and a shorty 3/8" drive ratchet for the places a air ratchet won't fit.
i did a write up on the repair a couple months back
pull the octane plug, you will never notice the power loss and will save the extra 92 octane cost

use a Ford SVC cd, has all the bolt sizes and diagrams of locations

 

Vango, removing the intake is not a big problem. I've done it a couple times already.

The last time I had bad pinging under load after engine warms up was due to heavy carbon fouling on the plugs, which was caused by a clogged EGO sensor (not leakiy injectors as I thought, but that could also happen). So check your spark plugs to see if they're all crudded up.

Build up in the intake manifold, especially behind the throttle plte, can come from the EGR as well. Hot exhaust gasses will bake any deposits onto the nearest surfaces. This will require use of a good cleaning solvent and a brush, as the usual jet spray from the cleaner is not strong enough to remove it.