Date: Thu, 21 Oct 1999 00:15:26 -0700
From: Justin VanAbrahams <jvanabranopsamnet>
Subject: Re: Mystery stalling


> Ken Washington wrote: > > > Check your vaccum hoses and throttle bypass valve (hooter valve). A few > > months ago I cleaned the plastic valve from the valve cover with hoses > > going to the throttle body. I was amazed at the chunks that cleared out. > > It helped my engine run noticeable cooler. The 'hooter valve' and the the throttle bypass valve are two very different things. The "hooter valve" is the cute name for the turbo bypass valve - essentially a vacuum diaphragm that redirects pressurized air from the throttlebody back to the low side of the turbo when the throttle plate snaps shut (like during a shift). The throttle bypass valve, as you'd see on some older cars, is replaced by the idle control valve, officially called the Adaptive Idle Control (AIC) valve. The former simply wears out and must be replaced, the latter is based around an electric motor, which can wear out or become clogged with debris. It can be cleaned and sometimes restored, but can wear out beyond repair. A sticky AIC could cause the stalling problem - it remains closed while your foot is on the gas, and is designed to open (to allow the car to idle) when you take your foot off the gas. As they age, grime can build up inside or the motor can become weak, causing the AIC to stick in the closed (or open) position. This will lead to idle irregularities. The plastic valve on the valve cover is simply a breather device. It allows hot air from the cylinder head to be evacuated and sucked back into the intake tract. This valve should not become clogged under normal circumstances, since it's only designed to suck air and nothing else. If you are still using dinosaur oil, oil residue and other related debris can become attached to the valve; it will ultimately dry out and coke up, restricting air flow out of the valve cover. This is a bad situation, and should not be allowed to continue. I believe cleaning and replacement of this valve is indicated in the normal scheduled maintenance. -Justin

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