This is a known problem with the IP. The dampner is inadequate, and the spring on the other end of the fuel rack gets weak with age, allowing the rack to vibrate fore and aft in sympathy with the longitudial vibration of the engine (only affects the 5 cylinder, by the way). I believe the internal design of the non-turbo IP is a bit different, so the effect is much less.
The cure is to adjust the dampner screw in slightly to reduce or eliminate the vibration, but you cannot overadjust, else it won't start cold! Also, eventually the vibration will get so bad it cannot be adjusted out. The real fix, an upgraged spring, requires complete disassembly of the IP to replace it, so I'd wait until something else needs fixed, too expensive. Peter
