re: Syncro running badly

Gday ALL,

Well after 2 years ownership and feeling smug I'd managed so far to
avoid the oft reported "syncro running badly, tearing my hair out"
scenario, my luck finally ran out yesterday.

Circumstances were that the syncro was running fine beforehand. So last
week I started and completed yesterday a rust repair/preventative
project to the metal floors of the rear cavity voids in behind the
tail-light assemblies.

I remain bemused as to the poor design by VW that allows dust, debris,
rain and hose water to freely enter the vehicle via both rearward side
vents (black louvres angled toward the sky), water gravitates down
internally and ends up on the cavity void floor with its many metal
joins and laps. There is no effective drainage system built in, the
water merely gravitates through those floor metal joins and laps, hence
a cause of rust in metalwork and seams in this vicinity over time. Nice
one VW.

To gain access, I stripped out all I could to both voids. In particular,
both rear tail-light assemblies, all accessible parts of the air intake
snorkel, the electronic control unit for idling stabilisation and the
air filter/debris collector assemblies. All were inspected, cleaned and
put back on completion of the project.

Started up the syncro from cold, it idled and revved normally for the
first "choke on" stage, after which it then started behaving erratically
(but without actually stalling), and sounding weird, with clatter from
the motor internals. Also what sounded like the occasional small
internal explosions, possibly in the area of the intake manifolds, when
attempting to rev the motor. By this stage there was NO effective
available power when trying to rev the motor, mostly the motor failed to
respond in the usual way, just idled badly and cycling short bursts of
revving then cutting back. There was no way the syncro could be driven
in that condition .... no meaningful power at all to drive away.

So now I'm at the "tearing hair out" stage. Shut it down, stripped out,
inspected, rechecked, reinstalled everything I'd previously taken out in
the project. Restarted the syncro .... same problem. More lost hair.

So now I'm thinking thousands of dollars to buy all the replacement
components to find the problem or have it towed to a knowledgable VW
mechanic somewhere.

Then I recalled Mark reporting on this forum that during his "syncro
running badly" episodes, someone thought to try disconnecting one of the
wires to the oxygen sensor. I figured I had nothing to lose, so why not
try that.

There are 3 wires for the O2 sensor. There is an obvious pair, one of
which has 12vdc, and also a separate single wire which showed about
1.7vdc. I tried all combinations of connect and disconnect. However,
when I disconnected the single wire .... VOILA!! .... the engine
returned to normal idling and power output. Took it for a run .... no

So really, I am none the wiser as to why this "running badly" happened
at all, nor why disconnecting the single O2 sensor wire fixed it.

For the record, a new O2 sensor was installed last September, the one
taken out was so badly deteriorated, it most likely had been there for a
very long time. Interestingly, installing the new O2 sensor made no
apparent difference whatever. Possible reason being, the internals of
the catalytic converter have probably long since disintegrated, so O2
sensor probably unable to sense correctly.

So for me, it's touch wood time again or else, maybe I need to find
religion .....