I ahve a 1994 Accord that when it idles it revs up and down. Sometimes it won't do it and sometimes it will. I think it might be a sensor. Please help. Thanks.

 

The most common cause of this problem is the Fast Idle Thermal Valve.
First thing is to be sure the coolant is full and block burped of air thru the 12mm bleed screw at the T-stat housing.
If that does not solve the problem, you might need to adjust the FITV; it lays sideways under the throttle body opening. There is a lid on it that is facing the fire wall.
Remove the lid and inside is a brass cone thru the middle of an adjusting screw.
You may need an inspection mirror to see inside.
Turn the screw in so that you hear no air bypassing when the engine is warmed up.

 

Is likely the fast idle valve, try removing it and cleaning it...make sure you remove the positive from battery before doing it...