Engine doing something VERY strange...

[jjguitar]

I was driving my car 2 days ago, going about 55 mph. I noticed that at one point, I heard the engine rev a little higher without me changing speed or gears. I took my foot off the accelerator, and the car actually stayed at the same speed and did not decelerate. After that, I hit the break to slow it down, which it did. However, as soon as I released the break, the car slowly accelerated again, without me even touching the gas! After about 10-20 seconds of doing this, I heard the engine slow down and go back to normal. This also happened once today.
It was as if the car's idle was very fast.

I first thought that it was the transmission, but my dad thinks it may have something to do with the computer. Does anyone know what is wrong with my car, how serious it is, and about how much it would cost to get repaired (or is it even worth getting fixed?)

My car is a 1987 Grand Marquis (5.0 L, 302 V8). It has about 133K on the engine. The transmission is rebuilt and is about 3-4 years old. I'm hoping this is no big deal. The car is running great otherwise.

Thanks,
Justin

[Neutrino]

i say either a sticky throtle or a faulty trotle position sensor

[Sluttypatton]

I'd have to agree with Neutrino, not a huge deal but it can be dangerous if not fixed.

[Racincc85]

yea, i agree. It's definatly a computer/sensor problem. My mom had a similiar problem in her 91 lumina. When you took your foot off the brake, the car would accelerate to 40 without touching the gas. It turned out to be a fried computer.

[Racincc85]

it could be the idle air control valve, i just talked to someone and they said this is a common problem among ford manufactured vehicles. good luck with fixing, hope all goes well