Hesitation on acceleration

Something is wrong with the car! It is a 1999 Pontiac Grand Prix GTP
with 90,000 miles.

I wasn't beating on it, nothing unusual. All of a sudden I thought I
felt a little hesitation when accelerating from about 40 - 60mph. I
didn't think anything of it. I pull into a shopping center and start
noticing that it is feeling very lumpy under idle (rolling at like
5-10mph). I had my foot on the brake and the rpms are going all over
the place, like down to 400 up to 1500, up down up down.

When I accelerate it hesitates then goes, hesitates then goes, etc.
Sometimes it will go smooth for a second, but for the most part there
is alot of hesitation. It finally stalled out when I was waiting in
line at taco bell. When I started it back up I noticed that the TCS OFF
was lit, and when I hit the TCS button, it would not toggle, it just
stayed off. This could have been happening before it stalled too, I
didn't notice.

The whole way home, I was getting the hesitation on acceleration. Easy
accel, hard accel, boost, no boost, didn't matter.

When I got home, I turned it off, and turned it back on, and the TCS
went back on, and I could toggle it as normal. I let her idle in park /
neutral for a bit, and notice the idle diving down to 3-400 then up to
12-1500 then back to 800ish where it would sit for a few, then dive
down and shoot up.

Something is really screwy!! Anyone know whats going on??? I just got
the damn car 200 miles / 5 days ago, so I don't know it's history, but
it has driven perfect until this!!

What is your engine/transmission combination?
That might help.

Supercharged 3.8L L67 motor. Not sure about the tranny. This problem
is not related to the tranny at all.

I'm leaning toward the problem being throttle position sensor or IAC
motor. I will be cleaning both, which will hopefully clear up the
problem.

Supercharged 3.8L L67 motor. Not sure about the tranny. This problem
is not related to the tranny at all.

I'm leaning toward the problem being throttle position sensor or IAC
motor. I will be cleaning both, which will hopefully clear up the
problem.

In case there is any interest or curiosity here, here is the update.

I took the car in for warranty (should have in the first place)
because, after all, I only put 200 miles on the car before there was
the problem.

The dealership was great about it, and fixed it right away.

Apparently it was a bad MAF sensor. I was going to clean this anyway if
I had cleaned under the hood, but they replaced it at no charge, and
now the car seems to be running fine!