It sounds counter-intuitive, but this is from my brother, who runs engines on dynomometers at Daimler-Chryslers' Tech Center. There is a possibility that the O2 sensor got too cold to respond properly. Sometimes, at sustained highway speeds, with a well tuned engine, the temp at the probe is not enough to keep the readings (voltage output) within required norms. Is the O2 sensor old? Older than, say, three years? Is the Westy driven regularly? Usually this happens on engines that have had custom or high-flow exhaust systems added, so unless you have removed your catalytic converter, and/or added an aftermarket muffler, this probably isn't it. The only reason that I mention this is the "1.5 hours sustained highway cruising" part of your troubleshooting list...

Mary Creasy <mkc1@LOCALNET.COM> wrote:
  Greetings List,
It's finally my turn to consult the list. I'm having a hesitation
problem which just surfaced. We were driving for about 1.5 hours and while
at cruising speed , a mild hesitation or dead spot in acceleration started
and got slowly worse until I stopped at a gas station and popped the hatch
to look and wiggle plugs, o2 wire and connection, idle stab. connections,
temp sensor 2 etc. After about 15 mins. we set out again to Christmas shop
and all was well. Starting and stopping all day, no problem. Return trip ,
all was well until about 1.5 hours or about 90 miles and it's back.
Progressively increasing but allowing me to get home. Got any ideas ? I
was having a drop in gas milage from almost 20mpg to 11mpg.
I guess I should tell you its a '85 1.9 wbx stock GL Westy. It's been
running fine until the mpg drop and now this.
I was poking around yesterday checking FI components to make sense of the
milage drop and got low resistance readings at temp sensor 2 . With the
temp as cold value should have been 5-6 k ohm and was just 1k.
Oh by the way, there was also a hard starting situation earlier this
week and that led me to check the cold start valve, temp sensor 2 and the o2
sensor. I think thats all the pertinent facts so humble me with your
wisdom.

Dave Creasy
'78 Westy
'85 Westy
'93 EVMV 5 sp.

Evan Mac Donald

1984 Wolfburg
1985 GL 7 Pass.
1991 Carat Weekender
1972 Chevy P/U
1993 Bonneville