Acceleration Pedal Issues

One of my cars, an 1987 Chrysler LeBaron GTS, which originally belonged to my mother and has all but 30K miles on it, on occasion while driving the accelerator pedal will go to the floor. (My mother took excellent care of the car - garaged -so much so that it looks factory new.) The first time this happened to me was last winter when I was coming off the exit ramp of the interstate and it was a long downhill ride to the light. I lightly put my foot on the accelerator to keep at the 30 mph exit speed and suddenly the pad went right to the floor. As soon as I applied the break the car slowed down. It freaked me out but I chalked it up as an anomaly due to icy roads, even though the car had on studded snow tires (2 years old on all 4 wheels). Then a few months later it happened again while on the highway. I immediately took it to my mechanic who could find nothing wrong (throttle, cable, motor mounts, etc.) - not even the floor mats were in the way. Despite that this still happens and has been increasing in frequency, to the point where I no longer drive the car. Any ideas on what can be causing this to help me figure it out? I really like the way this car drives and would love to keep it. Thanks for any advice and ideas.

When it goes to the floor does the engine rev or just stay the same. Does it come back up on its own or do you have to do something to get it back.

When it goes to the floor does the engine rev or just stay the same. Does it come back up on its own or do you have to do something to get it back.

When I lightly put my foot on the accelerator the pedal moves down real fast. I think I found a reason for the problem. I didn't even know this car had Cruise Control because I never bothered to read the manual and also because of where it is placed is not where it is on my other cars. On this car it is placed on the same stick with the turn signal and the windshield wipers. Someone else on another forum asked me if I had it. I ran out to the car and checked and sure enough it is there, called Speed Control, and was in the ON position.

According to the manual 'when you reach the desired speed you move the control to the ON position. This will establish memory and activate the system'. But the manual also says that breaking will deactivate the system without erasing the memory and I would have to push Resume to reactivate Speed Control. Only by 'Pushing the control to the OFF position or turning off the ignition erases the speed memory'. According to the manual the system only activates at 30 mph or above. But you are supposed to put the switch ON when you reach the desired speed for the system to engage. I don't know if it would engage itself by just having the switch in the ON position simply by turning on the car. One of the things the manual says that has me thinking is 'A sudden increase in engine rpm may be experienced if the clutch pedal is depressed while the speed control is engaged.' If that is the case can I assume that would cause the feeling that the accelerator pedal is moving down faster under my foot than I intended when I lightly depress the pedal?