Addressing other comments on this thread:
Rpmathis - the warpage is the major cause of your symptom.
Throttle body wear mentioned by Fred T - I am sure Fred knows when to install the bushings, but for others the design specification was a clearance of 0.004 ~ 0.006 inch (4 thousands to 6 thousands) as measured by a dial indicator from the throttle shaft to the throttle body in a direction perpendicular to the shaft. In practice, the "break-point" is 0.009 inch. If the wear is 0.009 or less, leave it alone. 0.010 or greater, install bushings.
Jon.
