1989 Mercury Sable, 3.0L V-6, Auto Trans. Engine Idles at about 2000 RPM.

Check the MAF sensor as well as the O2 sensor. With bad O2 sensor it is possible to have low rpm and loss in fuel economy.

Idle bypass screw adjustment or idle steper motor.

Don't know the issue

But that is the transmission coming out of gear

Not a good thing

I wouldn't drive it until a trans shop checked it out

Could be just torque converter lock-up (TCC)
solenoid

You should have a diagnostic performed to make sure you find the right problem. Otherwise, you could replace several things before finding the right one.

Sounds like you might have a stuck open EGR valve. Is the check engine light on. I would replace the fuel filter if it hasn't been replaced, also check the air filter.

Idle control sensor on thr trottlebody or if eequipped; airflow meter ...off the top of my head, hope it helps.

spray water with a windex type bbottle one the hoses till you see bubles

Probably need a fuel pump

yes about the upper intake and the only way i know how to check the coils is with a engine anilyser or if the check engine light comes on then you can have the codes pulled and that will tell you which cylender is missfiring this engine has a indevidual coil for each spark plug so thares 6 of them and thay slide right down over the sparkplugs

My wife had a 93 ford tempo 4 cylinder with same problem.It turned out to be the idle air solenoid mounted on the air intake manifold.