1994 RX 7 R-2 engine sputter

[badds]

I bought my RX 7 brand new in 1995. I have always had a tempermental engine. (I never knew what I was going to get when I accelerated.) I took it back to the dealership and even contacted corporate. They replaced spark plugs and wires. I was told there was nothing wrong and I could not convince them otherwise since it only occurred sometimes and at highway speeds. To date the problem was never resolved. Now if I try to accelerate say from 50 to 80 mph it sputters badly. It just occurred to me it might be the second turbo. Any suggestion?? By the way I have 39,000 actual miles.