DTC will set when the following conditions are present:

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1997 GMC Yukon, 1997 GMC Suburban, 1997 GMC Pickup, 1997 GMC Cab & Chassis, and 1997 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

Engine speed is less than 4000 RPM.
MAF sensor is at least 5 gm/s.
Crank sensor duty cycle is greater than 50 percent (or the ratio high ref/low ref is less than 1.8).
Engine speed displayed on scan tool is 2400 RPM.