Cadillac Repair: 99 cadillac devil just bought it but speedometer, digital speedometer, goin nuts

Question
QUESTION: car starts fine with no problems been sittin about a month or so and it runs good with no problems at all NO CHECK ENGINE light but after 30-45 minutes of driving the speedometer goes crazy then i slow down to less than 15mph or so i then  try to get the speed back up but i have to do it barely pushing on the accelerator if i step on it as normal the car will not respond just revs the engine even if i get it all the way down, the car will keep running (and not turn off) at low speed  not responding to how much gas i want, in other words i have to barely push then realease on the gas pedal repeting the process many times till i get the speed i want

now thats yesturday today the revin stopped i dont have to keep hittin the peddel to get gas or make the car go but the speedometer is still goin nuts on the highway could it the caddy had to reset itself after sittin so long?

really need to figure this out dont wanna lose money if any1 knows thanks

ANSWER: Do you have an ANALOG or DIGITAL speedometer ?.

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QUESTION: tnx alot for responding I have a digital speedometer now today the car been running good again just on the highway I hit like 55 it starts goin wacky still seems like it wants to work but right when I get off the highway it's fine again. So I'm hopping it's just takin time to get goin again cause it was sittin awhile the people who had it before me were old I think cause car is clean no check engine light either if that helps you out. But you think I should just keep drivin it on the highway to see if it goes to normal

ANSWER: I would just keep driving it until it either resolves itself and or the CHECK ENGINE light on the dash illuminates which will most likely be caused by the speedometer speed sensor located on the passengers side of the transmission which will need to be replaced.

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QUESTION: just this morning the check engine light came up if it's the problem you said is that expensive to repair hope not bro tnx for helpin out

Answer
Your problem is most likely the speedometer SENSOR mounted on the passengers side of the transmission which is accessed from under the vehicle. You should retrieve the CODE from the computer before replacing any components and after you replace said component, You will need to CLEAR the code from the computer.

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