95 240sx rev bouncing

[sr20det_s13]

My brother's s14 has been acting up for a month or 2 now. He cant go over 60mph or else his rpm starts to jump like crazy at 3k to 1k back up to 3k then back to 1k. And when you try to acclerate past 3k it starts to boggle. Sometimes it the engine stalls on itself its a automatic. My brother told me that it had the knock sensor code im not sure if that is the problem. Any input?

[aris_unlimited]

Have him reset the ECU and check for codes again. If the knock sensor code pops up again then that is definitely the first place to start.