> I'm sure glad I didn't spend Money on replacing my front heating core.  I
> hear it's spendy having a machanic put one in. All I really needed was a
> simple engine rebuild to relieve the back pressure from my cooling system.
> The pressure thing tends to happen when you have cracked heads.  So now that
> the heads have been replaced 3 times in the last 4 years.  I deceided to
> overhaul the bottom end by a very specialized machine shop.  The heater now
> blows hotter than I ever expected.  All for the small price of $2800 after
> taxes.
> Now the PROBLEM.
> When the engine is at idle for about 5 to 10 minutes, it starts getting real
> uneven, starts sputtering and stalls.  Is it the O2 sensor?.

A HA!  I had this same problem weeks ago on my 84!  Try disconnecting 
the O2 sensor and see if the problem goes away.  I found with my 84 
that disconnecting the O2 sensor caused the problem to disappear, and 
I did that for about a year until I had to pass emissions again.  
Took it into my friendly low-cost mechanic ;-) and he replaced the O2 
sensor etc. and when we connected the new sensor the problem was 
still there.  Finally bit the bullet and took it to VW and they 
diagnosed the problem as a collapsed crankcase breather hose.  They 
replaced the hose and reset all the basic engine settings (CO, 
timing, etc.) and the thing runs like a dream now.  Check that hose!

brian.