An issue on a 2003 Monte Carlo SS

So I'm planning on buying an 03' Monte Carlo SS from a buddy of mine. I
test drove it the other day and all was fine until I drove it a bit longer. It
seemed like it would accelerate a bit by its self and take a little bit longer to
shift. There were times where i would even be giving it gas and the rpms
would stick around 2-3,000 rpms. Even when I would be slowing down it
would be stuck around 3,000 and even when stopped. Oil looks okay and
can't check the transmission because it doesn't have a dipstick. We think it
may be idle air control. We are going to try and get it inspected soon, but any
ideas are appreciated. He has only driven it a few times and it usually just
sits since he drives a different car.