Iowa Chapter Director
Join Date: Jul 2002
Location: Ames, Iowa
when you turn the steering wheel it puts a lot of drag on the motor, so having the idle drop while turning the wheel is normal. The only reason it's making the engine shake is because your idle is lower than it should be already. I would also lean towards the Idle Air Control (IAC) being bad. You can try unplugging it while the car is at idle and seeing if the idle gets better or worse. If it gets better or doesnt change then it's bad.
1988 Notch Mustang: - 438W, direct port n2o, t56
2003 SVT Focus: - SCT X3 tuner