There is a bar going from the top of the engine.

Can you please retype that with some punctuation? I can read it three different ways and I want to get it right. Which engine do you have? Also, I assume you have an automatic transmission, but which one? There's a three-speed and a four-speed. If you don't know how to tell, with the four-speed there will be a circle around the "D" on the shift indicator on the floor or the dash.

That linkage that goes from the throttle body down to the transmission is called the "kick down" linkage. You'll see it move when a helper presses the gas pedal. That adjusts the fluid pressure that runs the shift valves. Higher pressures, such as when accelerating, increases the road speed needed to initiate an up-shift.

From your first description it sounded like the two shafts on the transmission were sticking together. Check them to be sure the one you're playing with moves freely and it returns freely under spring pressure. If it is sticking to the shifter shaft, it may be moving when you shift into drive. To the transmission that would be the same as shifting into drive while engine speed was very high. It will bang into gear but it will do that extra hard because line pressure will be higher than normal too.

If the shifter shaft and kick down shaft both move freely, it is likely there is internal damage inside the transmission. Check the fluid level and condition first. A whistling noise could be from the pump sucking up air instead of transmission fluid.

If it doesn't engage into drive when the engine is at idle speed, the clutch packs are not applying. That is due to insufficient fluid pressure. When increasing throttle valve pressure, as you're doing when you move the kick down linkage, makes it go into gear, that's usually because the pump is pumping a higher volume of fluid that overcomes the internal leakage in the clutch pack. With age and mileage the rubber lip seals on the pistons become hardened and brittle. That allows pressurized fluid to bypass the piston rather than put pressure on it to engage the clutch discs. My best recommendation if that appears to be the case is to get an opinion from a transmission shop. I have the same three-speed transmission in my '88 Grand Caravan daily driver and I use it once a year to drag a tandem axle enclosed trailer that's bigger than the van. These are really tough transmissions but when they need to be rebuilt, they aren't real difficult or expensive compared to most other automatics.