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Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Car
Satisfied Customers: 47662
Experience:  16 years of experience
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Jaguar Vanden Plas: 1997 Jaguar XJ Vanden Plas straight 6,104,000

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1997 Jaguar XJ Vanden Plas straight 6,104,000 miles. It is running rough and has a codes of multiple cylinder misfires/ random misfire. I have, so far, replaced alternator, spark plugs (ngk),replaced ignition coils,cleaned throttle body butterfly, and O2 sensors were replaced in the last 18 months have maybe 10k miles on them.Any Ideas as to what could be causing the rough idle?

Hello, I'm Chris. Thanks for visiting Just Answer.



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Customer: replied 3 years ago.

no answer yet

You mentioned rough running then rough idle, is it both?

Can you feel it misfiring and is it intermittent?

What is the engine running fuel pressure?



Customer: replied 3 years ago.

idle is some times smooth, sometimes rough.

on highway it will be smooth, get rough, check engine blinks, let off gas, and smooths out, re-apply gas, runs ok.


have not checked fuel pressure


seems to happen more when warmed up

When it gets rough on the highway, that's the misfire occurring so a fuel pressure test is needed. You will also ant to rule out dirty injector by doubling up on some STP cleaner in the fuel for a full tank. Once you have done this and ran the vehicle about 100 miles with the cleaner in it, let me know the fuel pressure while running.


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