I just bought my 2nd Jaguar XJ6 (40) 1993
the first one was a dream.. this one has started out as a nightmare.

The problem is that 20 mins after buying the car and driving it away it developed a very harsh up-shift on the Transmission.. the RPM doesn't spike and the car takes off well. When it hits 20 MPH the gear changes and its violent.. the other gears have started changing a tad harsher but not that noticeable. When coming to a stop.. when you hit the 20 mph mark its jerks again. What can be causing this issue?
Is this an easy fix like a solenoid problem or is this going to be a torque converter issue. Yes the light on the dash comes on. Once the car is cool.. there is no transmission issue or dash light. After driving for 20-30 mins.. that is when it starts up.. Please help anyone!

 

Well it seems that its not the Transmission.. but rather the micro processor that is causing the transmission to act up. Its also shut down the radio, the alarm and the air con.. hmm the wing mirrors too.. so no i have to get a new micro processor. But with that being said.. I eventually go onto the guy that sold the car and i am returning it and getting my money back.. so all has ended well