As the title suggests, I’m having an idle issue that isn’t exactly typical. I have a 1996 integra ls with a stock motor. It has a new distributor and alternator. The car first had a slight occasional surge from 1k-1.2k. It was throwing codes for the IAC, crank position sensor, and evap purge flow. I had the car serviced and had rear main seal, timing belt, water pump, oil pan gasket, and clutch all replaced. After I got it back I replaced both the IAC and evap purge solenoid. The car began surging up and down between 1k-2k non stop unless I’m driving and will continue if I take it out of gear. Also aggressively bucks the car back and forth if I drive at really low speeds. Now the car is only throwing codes for crank position sensor, and another one for P1508. I know that code can be for wiring but also about anything involving the intake. I just need some opinions on some strong possibilities and I can’t find anything specific to this scenario in the forums. Any input will help.