1999 Honda Civic P1337 and P1-336 Fault Codes: Causes and Fixes for Crankshaft Speed Fluctuation

My 1999 Honda Civic with 100,000 miles and a 4-cylinder automatic transmission has recently developed two diagnostic trouble codes: P1337 and P1336. The car was previously repaired after the crank pulley fell off; a crankshaft kit was installed by a local mechanic, and it ran fine until this week. The engine light turned on, and the vehicle began hesitating at stop signs. My student driver tried disconnecting and reconnecting the battery ground, which temporarily cleared the code—but the engine light reappeared quickly after. A short test drive was successful, but hesitation returned once she got back to her apartment. She has scheduled an appointment with the same mechanic (the only one with strong reviews in our area), who is currently installing a new sensor. The issue appears related to the Crankshaft Speed Fluctuation (CSF) sensor—P1337 indicates no signal from the CSF sensor, while P1336 shows intermittent interruption. These codes are often linked to or integral with the CKP (Crankshaft Position) sensor. A new vehicle is not an option due to cost and emotional attachment. I'm seeking advice on whether this is a common issue for 1999 Honda Civics, if there are alternative diagnostics, or if replacing the CSF/CKP sensor is the most reliable fix. Any insights would be greatly appreciated. Thank you in advance.