I put my 1989 Honda Prelude engine (auto) into a 1988 shell with manual transmission, and now my revs stay high only when driving and changing gears. Was wondering if it is a vacuum hose issue and how

check fluid levels add if low..change filter if clogged ..

The auto was notorious for clutch pack failure. Tolerances were tight in the inner workings and this caused inadequate oil flow and poor cooling. Sooner or later the auto transmissions fail. You could have the transmission rebuilt but that will cost a bit to do it so it wont break again. I might recomend going back to honda atf and changing the fluid again. If that does not work try an additive oil for the transmission. I had some sucess with the recomend product.

last resort, have it swapped to a manual transmission. This is a cheap alternative as f series transmissions from the accord can bolt up to the h22 and can be found cheap at the expense of higher gear ratios.

The fast idle valve is inside the throttle body. Sometimes it backs out and needs turned back in (it's threaded). This will cause the loping idle.

Get transmission filter changed with new fluid. Honda does not recommend transmission flushing.

dont put any fuel in any transmission

You can download the entire manual from www.pdftown.com
Here is the link to the shop manual for the 88 prelude that I used to do my Cam Belt.
http://pdftown.com/Honda-Prelude-1988-Service-Manual.html
Hope this helps...

Try changing the Transmission oil - can solve a host of problems, including rough changes.

tire rotation, air filter, breather element,
Inspections:
Timing belt for wear and tear
other belts be it V-belts or Serpentine
radiator fluid (older than 3 years needs a flush and fill)
transmission fluid and filter change. if its a manual transmission then change the gear oil
Battery inspection
Ignition system--- Spark plug gaps,wires,cap and rotor and coil inspection.
Motor Mounts inspection
Other things good for a car of that high of mileage are flushing out the old brake fluid and filling with new....same for power steering.
mostly inspections
Last but not least... put a can of Seafoam* into your gas tank and drive it on the highway for at least 30-45 minutes. congrats on your high mileage honda :-]

bro, i think your clutch is mess up. have it replace

Sounds like the pressure plate! Try this, rev the engine for a sec then when it starts to slows down try to put it in reverse - if the gears grind, its the pressure plate which will come with the clutch kit for about 125-175.00.

:0)

*rack and pinion is steering not trans! Separate issue??

Either: Your low on transmission fluid, you need to replace the filter, or there's something wrong with the transmission.