Rockwell Posted May 24, 2018 Share Posted May 24, 2018 This is a really weird one... 2011 Mack CXU613, 445 MP8, 580K miles. Whenever I set the Parking brake (yellow knob), my idle shoots way up. Set Brake, motor will idle at 650 RPM for about 5 seconds, then you hear the turbo begin to spool up and the motor revs up to 1200 rpm, as soon as it gets to about 1200rpm, you hear a slight and rapid thumping noise (almost as if the air compressor is kickin on?). At this point the motor will then fall back to 700 and idle normal. It will not do it again unless you release the parking brake and reapply. This ONLY happens when you set the yellow parking brake. Does not happen if I use trailer valve (red knob) to park. Does not happen if i drop to idle at a stop. Only when the yellow parking brake is engaged. This condition just suddenly started out of nowhere, nothing leading up to it. Other than that, everything else about the truck is aces. Starts, runs, pulls great! All temp/pressure gauges are normal. Any ideas anyone? Thank you Quote Link to comment Share on other sites More sharing options...
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