"Not Anyone We Know" > wrote in message
nk.net...
> Howdy folks. 96 Nissan Pathfinder. 3.3L V6 2WD. 151K on the odom.
Three

>
> So the surging/poor acceleration is gone. But here is the problem that
> remains. When the engine is cold, it starts and runs perfect. As it
warms
> up, everything is ok. After about 10-15 mins of driving I start getting a
> bad miss between 40 and 50 mph, real evident on cruise control. The
engine
> appears to be "hesitating". Here is the kicker. Disconnecting both front
> O2 sensors makes the problem go away. Both sensors are brand new Denso,
OEM
> style replacements.
>
> I can run all day with the O2 sensors unplugged (at the under hood wiring
> harness) and the engine runs perfect. Plug them back and I get:
>
> Cold engine: Good running engine
> Hot engine: Missing, stuttering, hesitation.
>
> What is the problem?

You probably have a vacuum leak. When the O2 sensors are unplugged the
computer sees a major fault and runs it rich. I would guess if you went
through
an emissions check it would be exceeding HC.

When it's hot the O2 sensors allow the computer to lean it down, and due
to your vacuum leak it's getting way too lean.

Ted