How does Throttle Body get so Dirty?

[ab_slack]

87 BII, 2.9L.

I pulled the air charge temperature sensor to see what the condition was and it was covered in oil and a gooey total mess.

I am guessing that is probably a reflection of how dirty the throttle body is there.

So how does the throttle body get all nasty like that? Only thing that occurs to me is sucking in some nasty stuff thru the PCV valve.

I recently found the PCV valve to be blocked when grommet was going bad. I am guessing it been that way a long time so any junk was probably pulled in before I got it.

Assuming there isn't another source for the grime in there.

 

[BRUTUS_T_HOG]

PCV system and EGR system introduces a lot of crap. Plus unlike a carbureted engine there is no fuel flowing through the intake to clean it.

 

[RonD]

All piston engines have blow-by.
When a cylinder fires some of that combustion "blows-by" the piston rings.
It is a very hot gas at that point and vaporizes some of the oil coating the cylinder walls.
And blow-by also increases the pressure in the crankcase and valve covers.

On older engines there was a metal tube in the lower block or upper oil pan that was pointed down at the ground, blow-by pressure went out that tube with the oil vapor and just dripped on the road.

PCV(positive crankcase ventilation) valve was added and that "dripping tube" was removed.
But there are two parts to the PCV system, one is often over looked, the Vent Hose.
The Vent Hose runs from the valve cover(opposite side from PCV valve on V6/V8 engines) to the air cleaner housing or Air Plenum(big air tube to upper intake).
The Vent Hose does two things, at lower RPMs when there is less blow-by and more vacuum the PCV valve sucks in more air than is available so Vent hose brings in fresh air, at higher RPMs when blow-by is high and vacuum is low Vent Hose allows extra blow-by out where it is sucked into the throttle body and upper intake.

This is most likely where that oil residue came from, if PCV valve gets clogged up then all the blow-by pressure and oil vapor is going out the Vent Hose.

 

[ab_slack]

Makes sense and both those were in very bad shape.