ECM failure

trying to get some help on my 1996 Toyota
Tacoma. My check engine light will come on while
running normal highway speed the truck would
then run real sluggish and backfiring the check
engine light will go off and everything would be
normal again. Decided to replace the throttle
position sensor and see if that will cure the
problem. No luck with the TPS. The check engine
light would not stay on indicating code stored in
the computer. Decided to hook my scanner up to it
to see if I could find anything on the live data are if
there were any code stored. There were no code
stored the scanner had no problem linking up with
the computer on the vehicle. Started the truck up
and was going to view live data while the truck was
running fine and the check engine light was not on.
While viewing the live data the check engine light
came on and the scanner lost communication with
the computer on the truck. the check engine light
went off and Communications was restored with
the scanner. It done this several times and every
time the check engine light come on I would lose
Communications with the computer on the truck.
Any help or solutions would greatly be appreciated.