Acceleration looping?

1981 Datsun 280ZX 5spd manual L28 IL6 SOC.

maintenance history unknown.

Today after a short drive and a bath the engine started looping after 2000 rpm.

The car idles fine while sitting but as soon as you push the gas the engine revs to 2k and then decelerates then back up to 2k then back down.The car does this with no hesitation until you take you foot off the gas then idles normal again.

Could this be a sensor issue? If so which one? The car didn’t start the problem until i bathed the engine area.

Check for vacuum leak.