1991 Camaro RS w/ 305 and 5 speed trans. Wierd problem. While driving at highway speed (or any cruise speed) not under a load car will stumble almost like shutting ignition on and off for a split second. Sometimes it will do it two or three times in a row. Car does not die. I recently noticed that the speedo jumps up right before it misses. For example if I am doing 70 not under load I noticed the speedo will jump to 90 then engine stumbles and returns to 70. I was thinking speed sensor? TPS sensor? electrical short?

It has been doing this for about a month and I drive around 60 miles round trip per day.

Any help or suggestions would be appreciated.

 

Run the car at night and watch under the hood for any spark plug wires that might be arching.