if youre engine is the 3300 V6 take a look at this
when it start to go up an down (the rpm) look the light on the transmission
P
R
N
D
2
1
the light near the P (when in park) will shut down when the trouble start
just press on the light and the light will goes on and 2 sec after the trouble will stop
it work for my in my GA '92 V6 3.3