Automation can improve the efficiency, reproducibility, and affordability of clinical immunodiagnostics, yet most ELISA automation platforms are bulky and expensive and remain poorly suited to decentralized, resource-poor settings. Enzymatic silver metallization immunoassays on low-cost glass or plastic slides enable multiplexed microscale measurements from a single drop of sample with a dry readout compatible with cellphone imaging, but fluid handling is still largely manual. We present AutoENZ, a low-cost, 3D-printed, modular immunoassay robot that executes customizable enzymatic metallization protocols with minimal user intervention. The user inserts a prepared diagnostic chip, loads the required reagents, and provides a protocol file, after which AutoENZ automates reagent delivery, washing, timed waiting, and drying steps to produce a metallized readout that can be quantified using a cellphone camera. AutoENZ is controlled by a microcontroller and uses integrated pumping, using inexpensive off-the-shelf components instead of custom microfluidics, for both continuous flow and calibrated microliter-scale dispensing. Built from accessible components, AutoENZ reduces hands-on time while maintaining quantitative performance. We validate AutoENZ using a model binding assay and multiplexed detection of antigen-specific antibodies in clinical tuberculosis samples, demonstrating its utility for affordable diagnostics in decentralized settings.