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Old July 21st 05, 04:10 PM
TeGGeR®
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"Elle" > wrote in
nk.net:


>
> You and I continue to disagree on this. A guzillion web sites back up
> my (along with like every other regular's) position on this.
>
>



I just tried two experiments on my own 1991 Integra just now.

-----------------------------

Firstly, I tried plugging the PCV hose shut. The idle dropped momentarily,
then climbed smoothly back up to 750 and remained there.

When I let go of the hose, the idle surged briefly, then settled back to
750rpm. As expected, the engine management system was adjusting air flow to
achieve correct idle speed.

-----------------------------

Secondly, with the car fully warm, I unplugged the PCV valve hose at the
pipe where it enters the intake manifold, so the PCV intake was completely
open as a massive air leak into the intake downstream from throttle plate.

The idle dropped momentarily, then began smoothly surging between 1,000rpm
and 2,500 rpm. As expected, the engine management system, crude as it is,
was attempting to adjust the mixture to be correct. The air leak being too
great, however, it was unsuccessful in doing so.

(Interestingly, air flow from the PCV valve itself stopped dead, suggesting
that ambient air pressure was keeping the valve shut. IOW, crankcase
pressure was lower than ambient.)

I then plugged the PCV intake pipe with my thumb, mimicking a plugged PCV
valve. The idle returned to a smooth 750rpm and stayed there.

I discovered that I could uncover up to a quarter of the PCV intake pipe
before the idle began surging again, the severity of the surging directly
related to the amount of exposed intake pipe.

-------------------------

Conclusion: Cars with engine management systems do not suffer noticeable
problems from a plugged or stuck-open PCV valve unless an extremely unusual
situation is present.

History:
I once had a 1975 Toyota Corolla with a carburetor and no feedback system.
This car would not idle at all with the PCV valve removed. Unlike the
Integras's feedback system, the carburetor was unable to compensate for the
excess air. I discovered this quite by accident when an aftermarket PCV
valve came apart on me.

--
TeGGeR®

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