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My 2002 Chevy Trailblazer that has 160,000 miles on it tends idle what I think is at a high rate when I start it(1500) and sounds like its roaring. It lasts about a minute then idles down to around 900. Sometimes the roaring noise will come back when I take off but doesn’t last very long. This only happens when it has sat for a long period of time. Is this something to be concerned with?

The roaring is a classic case of the electric fan clutch starting to go on the Trailblazer. The part alone is insanely expensive for a fan clutch (~$200) and a PITA to replace. If you can put up with the noise it could last awhile before croaking entirely. If the controller can’t set the fan speed, the SES light will go on and a code for the fan will be stored. The aftermarket Dorman replacement units have a lot of complaints so you might want to spring for the OEM unit if the time comes…

Thanks Twin Turbo! What does OEM stand for?

Original Equipment Manufacturer. Basically, the Chevy part. I put a Dorman in my 2004 and regretted it. The snout is slightly shorter and very difficult to install. Mine died a different death and stopped engaging. The new one roars for a brief period and sometimes does not disengage for a few miles (common complaints for the aftermarket units).

My TB has always had higher than expected idle since new. They run high as the A.I.R. pump and fan tests are being performed. You can tell when it’s having trouble controlling either when the high idle lasts longer than typical.