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Re: [T3] Idling Too Fast

On 2 Jun 2005 at 6:37, Tony Rongey wrote:

> I'm stuck.  I just rebuilt a '69 FI AT - all stock in
> a dual relief case.  I can't get it to idle below
> about 1200 after warmup.  Here's the current status:
> Voltage - 13.4
> Fuel Pressure - 29
> Dwell - 44
> Checked the trottle - it closes all the way, and the
> TPS is adjusted.
> Unmolested pressure sensor - holds vacuum.
> All hoses new and secure where they belong. No open
> vacuum ports.
> Aux Air working tested and working.
> I currently have it timed just a hair before TDC
> @1200rpm.
> Idle screw is closed all the way down.

The voltage is a bit low, but that's probably measured at idle and isn't the 
real number. It should get up close to 14 at med rpm, but, either way, that 
won't change your idle problem.

My guess is that you have a vacuum leak somewhere, but you just don't know 
where it is yet. That's really the only thing that can cause this.

Things to check: 

Is the idle still too fast once the aux air reg has warmed up and closed? You 
should be able to put your thumb over the AAR inlet with the engine warm and 
not notice any change in idle speed.

PS hose connected at the intake air dist end?

AT vacuum modulator hose connected at both ends?

CORRECT FI intake manifold gaskets (NOT the metal beetle ones) installed? Are 
the surfaces there clean and smooth with no dirt trapped that would hold the 
sealing surfaces apart?

If you used a later intake air distributor then you would need to have the cold 
start valve installed, and the very late IAD has an extra tube connected to the 
front plate that would let in a bit of extra air. (I doubt if it is either of 
these problems.)

It is important that you tighten down both intake air runners and the intake 
air distributor ONLY after you have pushed all of them together in the big 
short rubber connection hoses that seal them together. If you bolt the IAD down 
tightly and then install the pipes you'll find that there is stress between 
those parts that tends to hold those hoses open so they can't seal. I see a LOT 
of engines with hose clamps on these, but those are completely unnecessary, and 
probably counterproductive, if they are assembled with some thoughtfulness.

One way to look for vacuum leaks is to take an UNLIT propane torch and spray 
propane gas around suspicious places. Put some tape around the air inlet holes 
in the torch tip and this will make the tip spray almost pure propane. For big 
leaks, sucking in pure propane instead of air should make the engine run 
differently whenever the gas is sprayed over the area where the air is leaking 

Let us know what you find.

Jim Adney
Madison, WI 53711-3054

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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