One problem related to speed sensor has been reported for the 1999 Jeep Grand Cherokee. The most recently reported issues are listed below.
99 Jeep Grand Cherokee with engine problems customer states that the rpm's would immediately go up to the 200 or sometimes higher as soon as he starts up the car and also accelerate when the brakes are applied* the consumer stated various parts were replaced, however the problem returned. The consumers wife was driving, when all of a sudden the vehicle started to accelerate on its own, she applied the brakes as hard as she could, however the vehicle continued to proceed in a forward motion. The only solution was to place the vehicle into park. After placing the vehicle in park, the consumers wife placed it in drive again and immediately it started to accelerate uncontrollably. Applying the brakes with full force did not solve the problem. When aaa arrived and started the vehicle, nothing happened. The sudden acceleration happened again while the consumers daughter was driving. During one of the sudden acceleration incidents, the consumers wife was injured. The right front wheel speed sensor was replaced. The coolant radiator fan relay and water pump were replaced. The air bag light was on, the transmission seal was leaking. The fuel pump was replaced. The right and left hub bearing were replaced.