[V8] Flaky ECU Communication

[urq]

Lately on #2 I've been noticing that the car can get into a mode where it
has some major surging at over half throttle but less than WFO.  When I get
home I see a fails to control emission (don't remember actual text, but it
means the ECU can't lean it out) code; the car runs better after the code is
cleared.  I drove the car about 400 miles yesterday and I hooked up my
PDA/ProDiag.  Before getting started I tested to make sure I could connect,
but when the car was misbehaving I couldn't talk to the ECU.  On the way
home last night I left the carpet pulled up so that I could see the
interface communicating with the ECU ... It certainly appeared to be trying
to talk to the ECU.

I'm going to try swapping in another ECU just to see if it changes things,
but since the diagnostic plugs connect directly to the ECU I don't think
there's much else that could be wrong.  

Has anyone else noticed problems communicating with an ECU while the car is
being driven?  I've used the PDA before on shorter trips and have not had an
issue logging the data blocks ...

Steve B
San Jose, CA (USA)