On Tue, 24 Apr 2007 18:07:05 -0700, JR North
wrote:

Big 4 cyl engines are known for heavy idle. The automakers have known
for a long time the max size for acceptable idle smoothness is about
2.5 L. Above that, the shake from the power pulses is very large. You
can help it some by raising the idle speed to 900 RPM or so. The
engine's ECM may not allow this, and there is probably no actual
mechanical adjustment. See what the dealers lies suggest.

Don't those engines have harmonic balancers?