94 Cutlass Supreme 3.1 L V6.
The engine sputters ONLY when in PARK OR NEUTRAL.
Sounds like an intake or exhaust backfire.
It's not SUPER loud but it is very very noticeable.
Sometimes it won't do it but most of the time it does.
If you give it a quick rev and let off the accelerator, it will ALWAYS
do it (but ONLY in park or neutral) and much more loudly / violently.
At first I suspected bent or sticking valves but it
stops immediately when you put it into ANY gear (auto tranny). It will
not do it under any conditions when in gear, i.e., in gear at idle
speed, accelerating, decelerating, any constant speed, heavy load, hot
But as soon as it goes back into neutral or park, it does it
Due to that, I figure it is not sticky valves.???
It runs VERY well when in gear under all conditions.
Has about 129K miles on it with 80% highway miles.
Has always had Mobil 1 synthetic oil.
I took off the ignition computer and took it to NAPA.
They tested it 3 times consecutively (to make it get hotter each time)
and it passed each test.
Is there a different operating 'mode', via computer, that runs the
engine when in park or neutral versus when it is in gear?
Any help would be much appreciated.
Thanks in advance!
Mechanical Engineer and