The 1989 coach was built on a Gillig MHA chassis, Cat 3208 likely engine.
It has a pneumatic throttle, so there is a valve under your foot and an actuator under the bed.
You may just have a proken return spring.
Take the matress out and lay it on the couch, then remove 6 bolts with a 3/4 inch socket.
Place an old sheet across the edge of the platform.
Lift the cover and set it on the floor, be carefull the bottom will have soot on it.
Now look on the inside of the compartment on the engines side of the wall towards the front of the MH.
There is a round device with an air hose on one end, and a cable out the other.
The cable goes to the top of the engine to the injector pump/governer.
There should be some heafty springs on the throttle arm where the end of the cable is located, if you are lucky they have slipped off, if broken they need to be replaced.
Without a return spring the throttle can go high but no way to return to idle.
Also of note, the arm where the cable is attached is spring loaded to the arm coming out of the governer, it allows some flexibility in how the governer works, but if this spring breaks or weakens the coach may not shift out of first gear due to the engine not running fast enough.
Found that out the hard way...
Get the replacement springs from CAT, get the serail number from the engine and your Cat dealer can order what you need.
Tony & Lori
1989 Country Coach Savannah SE