1987 MR2 won't Rev

I have a 1987 MR2 that I just acquired and was planning to sell right away. I took it to the car wash, and when I went to leave, it wouldn't rev. It idles perfectly, but when it revs, it revs only to 1500rpm and then oscillates between this speed and idle. Let off the throttle and it idles perfectly still. Can anyone help me with this?

Thanks