Check for corosion on the EFI temp sensor, also when was the last time the
plugs were changed and what kind were used? And I wouldn't be so sure no
codes are set just because there is no CEL.

Had same issue on my girlfriend's 93 GXE several months ago.   The Check
Engine light on the instrument panel did not light up at all, but I followed
the procedure in the Chilton's manual for pulling error codes of the ECU.
It reported a faulty O2 sensor.  I replaced the sensor (located under the
car on the exhaust) and it has run like a charm since.

David

Try replacing the pressurized gas cap. Get the correct one - mine said
"pre-vented." Made my 92 SE stop all that rough running immediately. See my
post from today 9/6/2004 at 12:03 AM. called "Mystery Solved."

The cap cost me $5.99 or so. Easy to try this - it made my Max purr again.