When I'm driving at a steady speed the RPM's start surging from around 2000 to 3000 RPM's on its own. I can't feel any change in the gas pedal but can definately feel the car surging. It even does it when the cruise control is set. I've read where many 2006 owners have had the same problem but I haven't found what the answer is to get this fixed.
Engine Surge, spiking on 2006 Buick Rendezvous
by mike1814 in Berlin Heights, OH on February 23, 2011
ANSWER by dandd on February 25, 2011
Any service engine soon light on? If so , get those codes. I have also read some things about the crankshaft bolt coming loose which drives the crank shaft sensor crazy and can cause surging as well as poorly performing knock sensors driving the the timing very high which will also cause a surge. Have you asked Buick about this?