Chevrolet Express Knock Sensor Issue

The symptoms you describe, specifically the malfunction indicator illumination, increased fuel consumption, and uneven idling, are consistent with a malfunctioning knock sensor. Given your observation of corrosion on the cable or plug connection, it would be prudent to investigate this area further. Have you attempted to clean the contacts and apply dielectric grease to ensure a proper connection? What is the specific diagnostic trouble code being reported?

I haven't tried cleaning the contacts yet. I'll give that a go. The code it's throwing is P0325. If cleaning the contacts doesn't solve it, what would you recommend next?

The presence of a P0325 diagnostic trouble code corroborates the indication of a defective knock sensor within the engine management system. While cleaning the contacts may offer a temporary amelioration, it is unlikely to provide a permanent remedy if the sensor itself is compromised or the wiring harness is substantially damaged. Given the age of the vehicle, it may be advisable to have the vehicle inspected by a qualified technician. A workshop can properly diagnose and repair defective components. It might be the best course of action.

I cleaned the contacts like you suggested, but the light came back on after a day. I took it to a local shop, and as you suspected, the knock sensor was indeed faulty. They replaced it and the corroded connector – cost me 95€. Runs like a champ now. Thanks for pointing me in the right direction!