when u lift up off the gas car will slow down like u are steppen on the brake on 2000 Jaguar Vanden Plas

It happens all the while Iam driven

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2 answers
could be fuel filter issues or transmission as if it's in 1st gear? also check basic filters like air and fuel... less expensive to replace.
I just bought my 05 jag,if it is in sport mode ,u can drive normally ,but the car will de-accelerate quickly unlike if it was in normal drive.