well i'm not sure where it is exactly

but i'm thinking the idle up thing for the auto when you change from N to D etc is defective

Mrnickleye... does this item exist? i should imagine it does... would that be in the nsw or auto ecu?
got the same prob on a nissan bluebird but it still runs fine just vibrates like hell lol

Well...is the vibration due to low idle in gear? Outa gear?

The ECU (computer) recognizes when car is in gear and adjusts idle through the ISC (idle speed control) valve. (This may be called something else in the Celica, but its the same thing).

The vibration could be caused by 1 or 2 cylinders with poor spark. Pull wires one at a time while idling to see if a cylinder is weak, and does not make the engine act rough. (good ones make the engine run rough when the wire is removed. Don't shock yourself, use special pliers)

But more likely a fuel or air issue. Perhaps a vacuum leak. Most vacuum leaks only effect 1-2 cylinders, and then usually at idle.

Check that all the vacuum hoses are ok. Then, while idling, spray some brake cleaner along the intake manifold at the head, and other gaskets on it.

You have to do a fuel pressure test to see if an injector is leaking.

Do the other stuff first, cause you might solve the problem. If not, then a shop is best equipped to test the fuel system.

checkthe unis in the drive shaft:)