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Hello, I am looking for some help on my 93 Jaguar XJ6 with a 4.0..  It will start right up and idle fairly well but it will not accelerate.  If you ease the gas pedal it will open up but not if you step on the gas like you normally would.  When you do, it misses and backfires into the intake.  Acts like either it is running to lean or that the ignition timing is off.  The other thing is, if you reset the computer (by unhooking the battery) and then start it, it runs really good for a few minutes and then starts to act up..  Almost as if a sensor someplace is affecting the computer but not sure which one or if I should be looking more at the fuel or the ignition..  Any suggestions??  Could it be the electronic spark sensor that sits on the timing cover?  Could it be shorting our?  What is the best way of testing it and the rest of the components?  Any help is greatly appreciated.