Does anyone know how to intentionally disable the VCC from lock-up? I an trying to diagnose a problem with a shudder at 28 mph. I get a mild shudder at 28 mph and sometimes above that speed. It only happens after the engine/tranmission has warmed up. It seems to happen after the VCC has locked up because if I tap the brake after the shudder, the RPM increases. Should the VCC be engaging at speeds in the low 30 mph?

1996 deville, 121K, no DTC codes of any kind.

VCC engages at 41 MPH as I recall. Have you replaced plugs & wires? Have you had the fuel rail recall done? A misfire after the recall is very common. Been there, done that. New OEM wires curred the problem for me.

I had the fuel rail replaced last year. After the replacement, the car cranked longer than before on initial start-up in the morning. I replaced the plugs and that solved the longer cranking time for start-up. I checked the spark plug wire resistance when I relaced the spark plugs per the Chilton manual. The resistance was OK per the Chilton manual, so I didn't repalce the wires.

My problem always seems to occur around 28 mph. A 1/2 second "shudder". I know that the VCC is locking up at less than 41 mph. Seems to lock-up in the low 30 mph.

The switch on the brake peddle if you could close that switch then the VCC should not lock up but you would have brake lights on. I guess it would be ok for a short term test run.........You would know if the shudder was caused by the locking up of the VCC............Not sure how you would keep the switch made..........Let us know.........Jim