Help: O2 sensor & idle

[Cory_Langford at bcit.ca (Cory Langford)]

Well,

Everything is almost perfect with the '78 again.  I have a couple small 
issues to finish up.

1st.  The air/fuel gauge is no longer working.  I figured the o2 sensor 
must be on the way out, so I connected up the old trusty multi meter and 
ran it around for a few days.  As soon as the o2 sensor warms up it start 
giving out some really strange readings.  I currently idle at -180 mV - so 
does that mean my car is so efficient it actually absorbs emissions? :)

I have never seen an o2 sensor go into the -ve.  So Just figured I would 
check with the list to make sure there is not something else that could be 
causing the issue.  For the 1st 5-10 minutes it reads correctly and then 
swings over to the -ve range.  Reading between -180 when idle to -900 when 
you really lean into it..

Before I go and replace it again, I was wondering what the leading causes 
of o2 sensor failure are?  When I dropped the '78 back on the road I 
invested in a new o2 sensor just to make sure it would be working for a 
while.  Granted it was only a 1 wire, but for a bosch 1 wire to last less 
than 3 months, something must be killing it.



2nd:  A rather strange thing I can't quite figure out with the idle.  I 
have ended up overhauling the entire fuel system except for the fuel 
distrib (pump, filter, injectors, pressure reg all new).  In the process I 
have disconnected the cold start injector and the aux air valve.  When 
really cold it take just a little coaxing to start, but that is expected 
with the cold start removed at the moment. 

The thing that is strange is when I start it up and the engine is cold, 
the idle jumps up to 1800.  Once it gets to normal operating temp, the 
idle drops down to a nice 1000.  I can't figure out what is causing the 
idle to jump.  There is no aux air to allow it to idle higher, and no cold 
start inj to give it more fuel.  There is nothing I can think of that is 
acting on cold and not on hot.  All I can think is the engine is actually 
running better cold than hot. 

Anyone want to take a stab at that one :)


On a side note, for those mk1 owners doing projects this spring.  I may 
end up buying another mk1 shell that is in rough shape, but it will mean I 
may end up with an extra Zender front grill (the badgless one), a Zender 
rear hatch wing and possibly a set of Zender side skirts.

Cory Langford
'86 Roc turbo, 
'78 Roc turbo - Daily driver project,
'65 Ghia Coupe
95 Eurovan, etc, etc... :)