Positive Crankhouse Ventilation Video!
Found some air pressure coming up in Oil Filler Cap so decided to check out the PCV valve.
Seems to be a common problem on the Previas. It's a pretty simple procedure to check and clean it.
Watch this video. If you find it useful I hope you give a thumbs up!
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Good instruction for PCV.
----------------------- From yotatech forum ----------------
Originally Posted by brentcole5
negative pressure because after i took the cap off and noticed the idle drop i just set the cap back on and the idle picked up again
That's correct operation, and confirms your PCV(Positive Crankcase Ventilation)valve IS functioning. You'd notice the same thing if you removed the PCV valve hose with the engine running too.
Here's why.
Your PCV valve is a one-way valve in a rubber hose connected to the valve cover at one end and your air intake at the other. O.k., so when your engine is running the intake is sucking on that hose through the PCV valve as it sucks air into your engine. Some air from the intake is also blown simultaneoulsy into the crankcase through another hose creating a positive pressure flow, out of the crankcase, of blow-by gasses through the PCV valve into the intake. Whatever blow-by gasses sucked, through the PCV valve, out of the crankcase get recycled back into the combustion process through the intake.
This system causes a vacuum(negative pressure)under the valve cover due to the constrictions in the flow of the blow-by gasses from the crankcase to the PCV valve. When you remove the oil cap(while the engine is running)and break the valve cover's air-tight seal it prohibits that from occuring. This creates a vacuum leak. Vacuum leaks cause your idle to lower and usually make the engine struggle to run at all.
https://www.yotatech.com/forums/f116/oil-cap-idle-change-126506/
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