emission testfailed,HC was 422 to be 220 loaded,idle was1084 to be 220.CO good on 1990 Toyota Supra

did a complete tune runs good at idle,now right at 2000 rpm's it cuts on and off,you can slow it dowm and it will rev higher but it won;t hold.why does it pulse back and forth ?

Asked by for the 1990 Toyota Supra
you say at 2K rpms itcuts on and off. Is it like the rev-limiter is kicking in? If so get it scanned by a shop that will be able to read 'live' data and see what the sensors are doing. A wild guess would be a dead spot in the TPS , but that's a wild guess.Put a vacuum guage on it and watch and record the readings and whether it's steady or smooth , and reply with that info if the scanner bit is unavailable.
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Check for vacuum leaks if your idle is surging erratically.