1987 Crown Vic engine races

I have a 1987 Ford Crown Vic. The engine will suddenly race for no apparent reason and then it stops racing and runs fine. I have changed the computer but that didn't fix it. I have a feeling it is a sensor, but which one? Also, it seems to only happen when the weather turns chilly. I have had the car sitting at a stop sign and it will suddenly lurch forward. Needless to say, I always have my foot solidly on the brake. If you have a solution, please e-mail snipped-for-privacy@aol.com. Thanks. rd