System Too Lean
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1992 Pontiac Firebird, 1992 Oldsmobile Custom Cruiser, 1992 Chevrolet Caprice, 1992 Chevrolet Camaro, and 1992 Cadillac Brougham. However, it is still accessible from the selected car via links, so may be relevant.
If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary up and down; disconnecting IAC may not help. "Scan" and/or digital voltmeter (10-megohm) will read an oxygen (O2) sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in fuel. A contaminated O2 sensor (caused by silicone) will produce lean air/fuel mixtures with an O2 sensor output fixed greater than 800 mv (.8 volt). This may also set Code 45.