[T3] Problem starting / warming up

[Jim Adney]

On 26 Sep 2012 at 18:40, Joshua MacDonald wrote:

> My '70 fastback has recently begun behaving as follows (in Mountain View, CA):
> 
> It turns over and fires up, revs to idle speed, then abruptly stops firing,
> the engine speed free-falls by maybe 25%,
> then it starts firing again. The process repeats for several
> minutes--idling up, free falling down, ...

This sounds like what typically happens if the idle is set too high. 
The FI is programmed to automatically turn off the injectors if the 
RPM rises above something like 1400 and stay off until it falls back 
below something like 1100. 

> The engine sounds normal on the upswing. The free-fall sounds just
> like it does after cutting-off the ignition.
> If I depress the accelerator, the engine revs faster but free falls
> just the same.
> After a couple of minutes, depressing the accelerator will rev to a
> higher RPM than at initial start-up, but still the same free-fall.

If the throttle valve switch (TVS) is adjusted properly, this 
behavior should stop as soon as the throttle is off idle. Try 
unplugging the TVS: this will make the FI think you're no longer at 
idle. If this stops the behavior, then everything is normal except 
that your idle speed has been set too high and the TVS is either 
broken or misadjusted. (most likely the latter.)

> Eventually, it resolves, I assume because the engine has warmed up.
> During the idle-up/free-fall cycle, I possibly hear the sound of a
> relay switching on/off under the dash. It's also possible the the
> battery voltage is a bit low.

While it's doing this, is it possible to get it out on the road and 
driving? If so, your answer is above. If not, you have a larger 
problem.

If the relay under the dash is actually switching on and off, this is 
a different problem. For that, the first thing I'd check would be to 
make sure that the screw holding the relay under the back seat is 
tight.

Check your battery voltage at medium rpm after a good drive to warm 
everything up. It should be 14.1 - 14.4 V, measured across the 
battery. It will be 1/2 V higher at the generator and 1/2 V lower if 
you measure at the fuse box.

If it's below 13.5 V at the battery, replace the voltage regulator.

 If it is below 
-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************