I have been checking my timing on my 93 NX2K. I have disconnected the TPS and revved the engine to 3000 RPM 3 times as the directions say. When the fan is running it reads between 12-14 degrees. When the fan stops it reads 15-17 degrees. Is it normal for the reading to change when the fan comes on? Should I try to set it for what it reads when the fan is on or off? Thanks.